Skip to main content
Create new
Introduction
Reactivity
Props
Logic
Events
Bindings
Lifecycle
Stores
Motion
Transitions
Animations
Easing
SVG
Actions
Classes
Component composition
Context API
Special elements
Module context
Debugging
7GUIs
Miscellaneous
App.svelte
Butterfly.svelte
<script>
import Butterfly from './Butterfly.svelte';
let count = $state(0);
let doubled = $derived(count * 2);
let quadrupled = $derived(doubled * 2);
let octupled = $derived(quadrupled * 2);

function flap() {
count += 1;
}

$effect(() => {
// Because of this line, clicking the butterfly will cause information
// to be logged to the console about which state changed to cause
// the effect to re-run. (note: stack traces are better
// outside the playground!)
$inspect.trace();
if (octupled > 20) {
alert('The flapping of the wings of a butterfly can be felt on the other side of the world.')
}
});
</script>

<Butterfly onflap={() => count += 1} />

Error compiling component

WebAssembly.instantiateStreaming(): value type opcode @+13
import "svelte/internal/disclose-version";
import * as $ from "svelte/internal/client";
import Butterfly from './Butterfly.svelte';

export default function App($$anchor, $$props) {
$.push($$props, true);

let count = $.state(0);
let doubled = $.derived(() => $.get(count) * 2);
let quadrupled = $.derived(() => $.get(doubled) * 2);
let octupled = $.derived(() => $.get(quadrupled) * 2);

function flap() {
$.set(count, $.get(count) + 1);
}

$.user_effect(() => {
if ($.get(octupled) > 20) {
alert('The flapping of the wings of a butterfly can be felt on the other side of the world.');
}
});

Butterfly($$anchor, {
onflap: () => $.set(count, $.get(count) + 1)
});

$.pop();
}
result = svelte.compile(source, {
generate: ,
});
/* Add a <style> tag to see the CSS output */
		
			
				
  • Root {
    • css: null
    • js: []
    • start: 646
    • end: 685
    • type: "Root"
    • fragment: Fragment {...}
      • type: "Fragment"
      • nodes: [...] (2)
        • Text {...}
          • type: "Text"
          • start: 644
          • end: 646
          • raw: "\n\n"
          • data: "\n\n"
          }
        • Component {...}
          • type: "Component"
          • start: 646
          • end: 685
          • name: "Butterfly"
          • attributes: [...] (1)
            • Attribute {...}
              • type: "Attribute"
              • start: 657
              • end: 682
              • name: "onflap"
              • value: ExpressionTag {...}
                • type: "ExpressionTag"
                • start: 664
                • end: 682
                • expression: ArrowFunctionExpression {...}
                  • type: "ArrowFunctionExpression"
                  • start: 665
                  • end: 681
                  • loc: {...}
                    • start: {...}
                      • line: 26
                      • column: 19
                      }
                    • end: {...}
                      • line: 26
                      • column: 35
                      }
                    }
                  • id: null
                  • expression: true
                  • generator: false
                  • async: false
                  • params: []
                  • body: AssignmentExpression {...}
                    • type: "AssignmentExpression"
                    • start: 671
                    • end: 681
                    • loc: {...}
                      • start: {...}
                        • line: 26
                        • column: 25
                        }
                      • end: {...}
                        • line: 26
                        • column: 35
                        }
                      }
                    • operator: "+="
                    • left: Identifier {...}
                      • type: "Identifier"
                      • start: 671
                      • end: 676
                      • loc: {...}
                        • start: {...}
                          • line: 26
                          • column: 25
                          }
                        • end: {...}
                          • line: 26
                          • column: 30
                          }
                        }
                      • name: "count"
                      }
                    • right: Literal {...}
                      • type: "Literal"
                      • start: 680
                      • end: 681
                      • loc: {...}
                        • start: {...}
                          • line: 26
                          • column: 34
                          }
                        • end: {...}
                          • line: 26
                          • column: 35
                          }
                        }
                      • value: 1
                      • raw: "1"
                      }
                    }
                  }
                }
              }
            ]
          • fragment: Fragment {...}
            • type: "Fragment"
            • nodes: []
            }
          }
        ]
      }
    • options: null
    • instance: Script {...}
      • type: "Script"
      • start: 0
      • end: 644
      • context: "default"
      • content: Program {...}
        • type: "Program"
        • start: 8
        • end: 635
        • loc: {...}
          • start: {...}
            • line: 1
            • column: 0
            }
          • end: {...}
            • line: 24
            • column: 0
            }
          }
        • body: [...] (7)
          • ImportDeclaration {...}
            • type: "ImportDeclaration"
            • start: 10
            • end: 53
            • loc: {...}
              • start: {...}
                • line: 2
                • column: 1
                }
              • end: {...}
                • line: 2
                • column: 44
                }
              }
            • specifiers: [...] (1)
              • ImportDefaultSpecifier {...}
                • type: "ImportDefaultSpecifier"
                • start: 17
                • end: 26
                • loc: {...}
                  • start: {...}
                    • line: 2
                    • column: 8
                    }
                  • end: {...}
                    • line: 2
                    • column: 17
                    }
                  }
                • local: Identifier {...}
                  • type: "Identifier"
                  • start: 17
                  • end: 26
                  • loc: {...}
                    • start: {...}
                      • line: 2
                      • column: 8
                      }
                    • end: {...}
                      • line: 2
                      • column: 17
                      }
                    }
                  • name: "Butterfly"
                  }
                }
              ]
            • source: Literal {...}
              • type: "Literal"
              • start: 32
              • end: 52
              • loc: {...}
                • start: {...}
                  • line: 2
                  • column: 23
                  }
                • end: {...}
                  • line: 2
                  • column: 43
                  }
                }
              • value: "./Butterfly.svelte"
              • raw: "'./Butterfly.svelte'"
              }
            }
          • VariableDeclaration {...}
            • type: "VariableDeclaration"
            • start: 57
            • end: 79
            • loc: {...}
              • start: {...}
                • line: 4
                • column: 1
                }
              • end: {...}
                • line: 4
                • column: 23
                }
              }
            • declarations: [...] (1)
              • VariableDeclarator {...}
                • type: "VariableDeclarator"
                • start: 61
                • end: 78
                • loc: {...}
                  • start: {...}
                    • line: 4
                    • column: 5
                    }
                  • end: {...}
                    • line: 4
                    • column: 22
                    }
                  }
                • id: Identifier {...}
                  • type: "Identifier"
                  • start: 61
                  • end: 66
                  • loc: {...}
                    • start: {...}
                      • line: 4
                      • column: 5
                      }
                    • end: {...}
                      • line: 4
                      • column: 10
                      }
                    }
                  • name: "count"
                  }
                • init: CallExpression {...}
                  • type: "CallExpression"
                  • start: 69
                  • end: 78
                  • loc: {...}
                    • start: {...}
                      • line: 4
                      • column: 13
                      }
                    • end: {...}
                      • line: 4
                      • column: 22
                      }
                    }
                  • callee: Identifier {...}
                    • type: "Identifier"
                    • start: 69
                    • end: 75
                    • loc: {...}
                      • start: {...}
                        • line: 4
                        • column: 13
                        }
                      • end: {...}
                        • line: 4
                        • column: 19
                        }
                      }
                    • name: "$state"
                    }
                  • arguments: [...] (1)
                    • Literal {...}
                      • type: "Literal"
                      • start: 76
                      • end: 77
                      • loc: {...}
                        • start: {...}
                          • line: 4
                          • column: 20
                          }
                        • end: {...}
                          • line: 4
                          • column: 21
                          }
                        }
                      • value: 0
                      • raw: "0"
                      }
                    ]
                  • optional: false
                  }
                }
              ]
            • kind: "let"
            }
          • VariableDeclaration {...}
            • type: "VariableDeclaration"
            • start: 81
            • end: 115
            • loc: {...}
              • start: {...}
                • line: 5
                • column: 1
                }
              • end: {...}
                • line: 5
                • column: 35
                }
              }
            • declarations: [...] (1)
              • VariableDeclarator {...}
                • type: "VariableDeclarator"
                • start: 85
                • end: 114
                • loc: {...}
                  • start: {...}
                    • line: 5
                    • column: 5
                    }
                  • end: {...}
                    • line: 5
                    • column: 34
                    }
                  }
                • id: Identifier {...}
                  • type: "Identifier"
                  • start: 85
                  • end: 92
                  • loc: {...}
                    • start: {...}
                      • line: 5
                      • column: 5
                      }
                    • end: {...}
                      • line: 5
                      • column: 12
                      }
                    }
                  • name: "doubled"
                  }
                • init: CallExpression {...}
                  • type: "CallExpression"
                  • start: 95
                  • end: 114
                  • loc: {...}
                    • start: {...}
                      • line: 5
                      • column: 15
                      }
                    • end: {...}
                      • line: 5
                      • column: 34
                      }
                    }
                  • callee: Identifier {...}
                    • type: "Identifier"
                    • start: 95
                    • end: 103
                    • loc: {...}
                      • start: {...}
                        • line: 5
                        • column: 15
                        }
                      • end: {...}
                        • line: 5
                        • column: 23
                        }
                      }
                    • name: "$derived"
                    }
                  • arguments: [...] (1)
                    • BinaryExpression {...}
                      • type: "BinaryExpression"
                      • start: 104
                      • end: 113
                      • loc: {...}
                        • start: {...}
                          • line: 5
                          • column: 24
                          }
                        • end: {...}
                          • line: 5
                          • column: 33
                          }
                        }
                      • left: Identifier {...}
                        • type: "Identifier"
                        • start: 104
                        • end: 109
                        • loc: {...}
                          • start: {...}
                            • line: 5
                            • column: 24
                            }
                          • end: {...}
                            • line: 5
                            • column: 29
                            }
                          }
                        • name: "count"
                        }
                      • operator: "*"
                      • right: Literal {...}
                        • type: "Literal"
                        • start: 112
                        • end: 113
                        • loc: {...}
                          • start: {...}
                            • line: 5
                            • column: 32
                            }
                          • end: {...}
                            • line: 5
                            • column: 33
                            }
                          }
                        • value: 2
                        • raw: "2"
                        }
                      }
                    ]
                  • optional: false
                  }
                }
              ]
            • kind: "let"
            }
          • VariableDeclaration {...}
            • type: "VariableDeclaration"
            • start: 117
            • end: 156
            • loc: {...}
              • start: {...}
                • line: 6
                • column: 1
                }
              • end: {...}
                • line: 6
                • column: 40
                }
              }
            • declarations: [...] (1)
              • VariableDeclarator {...}
                • type: "VariableDeclarator"
                • start: 121
                • end: 155
                • loc: {...}
                  • start: {...}
                    • line: 6
                    • column: 5
                    }
                  • end: {...}
                    • line: 6
                    • column: 39
                    }
                  }
                • id: Identifier {...}
                  • type: "Identifier"
                  • start: 121
                  • end: 131
                  • loc: {...}
                    • start: {...}
                      • line: 6
                      • column: 5
                      }
                    • end: {...}
                      • line: 6
                      • column: 15
                      }
                    }
                  • name: "quadrupled"
                  }
                • init: CallExpression {...}
                  • type: "CallExpression"
                  • start: 134
                  • end: 155
                  • loc: {...}
                    • start: {...}
                      • line: 6
                      • column: 18
                      }
                    • end: {...}
                      • line: 6
                      • column: 39
                      }
                    }
                  • callee: Identifier {...}
                    • type: "Identifier"
                    • start: 134
                    • end: 142
                    • loc: {...}
                      • start: {...}
                        • line: 6
                        • column: 18
                        }
                      • end: {...}
                        • line: 6
                        • column: 26
                        }
                      }
                    • name: "$derived"
                    }
                  • arguments: [...] (1)
                    • BinaryExpression {...}
                      • type: "BinaryExpression"
                      • start: 143
                      • end: 154
                      • loc: {...}
                        • start: {...}
                          • line: 6
                          • column: 27
                          }
                        • end: {...}
                          • line: 6
                          • column: 38
                          }
                        }
                      • left: Identifier {...}
                        • type: "Identifier"
                        • start: 143
                        • end: 150
                        • loc: {...}
                          • start: {...}
                            • line: 6
                            • column: 27
                            }
                          • end: {...}
                            • line: 6
                            • column: 34
                            }
                          }
                        • name: "doubled"
                        }
                      • operator: "*"
                      • right: Literal {...}
                        • type: "Literal"
                        • start: 153
                        • end: 154
                        • loc: {...}
                          • start: {...}
                            • line: 6
                            • column: 37
                            }
                          • end: {...}
                            • line: 6
                            • column: 38
                            }
                          }
                        • value: 2
                        • raw: "2"
                        }
                      }
                    ]
                  • optional: false
                  }
                }
              ]
            • kind: "let"
            }
          • VariableDeclaration {...}
            • type: "VariableDeclaration"
            • start: 158
            • end: 198
            • loc: {...}
              • start: {...}
                • line: 7
                • column: 1
                }
              • end: {...}
                • line: 7
                • column: 41
                }
              }
            • declarations: [...] (1)
              • VariableDeclarator {...}
                • type: "VariableDeclarator"
                • start: 162
                • end: 197
                • loc: {...}
                  • start: {...}
                    • line: 7
                    • column: 5
                    }
                  • end: {...}
                    • line: 7
                    • column: 40
                    }
                  }
                • id: Identifier {...}
                  • type: "Identifier"
                  • start: 162
                  • end: 170
                  • loc: {...}
                    • start: {...}
                      • line: 7
                      • column: 5
                      }
                    • end: {...}
                      • line: 7
                      • column: 13
                      }
                    }
                  • name: "octupled"
                  }
                • init: CallExpression {...}
                  • type: "CallExpression"
                  • start: 173
                  • end: 197
                  • loc: {...}
                    • start: {...}
                      • line: 7
                      • column: 16
                      }
                    • end: {...}
                      • line: 7
                      • column: 40
                      }
                    }
                  • callee: Identifier {...}
                    • type: "Identifier"
                    • start: 173
                    • end: 181
                    • loc: {...}
                      • start: {...}
                        • line: 7
                        • column: 16
                        }
                      • end: {...}
                        • line: 7
                        • column: 24
                        }
                      }
                    • name: "$derived"
                    }
                  • arguments: [...] (1)
                    • BinaryExpression {...}
                      • type: "BinaryExpression"
                      • start: 182
                      • end: 196
                      • loc: {...}
                        • start: {...}
                          • line: 7
                          • column: 25
                          }
                        • end: {...}
                          • line: 7
                          • column: 39
                          }
                        }
                      • left: Identifier {...}
                        • type: "Identifier"
                        • start: 182
                        • end: 192
                        • loc: {...}
                          • start: {...}
                            • line: 7
                            • column: 25
                            }
                          • end: {...}
                            • line: 7
                            • column: 35
                            }
                          }
                        • name: "quadrupled"
                        }
                      • operator: "*"
                      • right: Literal {...}
                        • type: "Literal"
                        • start: 195
                        • end: 196
                        • loc: {...}
                          • start: {...}
                            • line: 7
                            • column: 38
                            }
                          • end: {...}
                            • line: 7
                            • column: 39
                            }
                          }
                        • value: 2
                        • raw: "2"
                        }
                      }
                    ]
                  • optional: false
                  }
                }
              ]
            • kind: "let"
            }
          • FunctionDeclaration {...}
            • type: "FunctionDeclaration"
            • start: 201
            • end: 235
            • loc: {...}
              • start: {...}
                • line: 9
                • column: 1
                }
              • end: {...}
                • line: 11
                • column: 2
                }
              }
            • id: Identifier {...}
              • type: "Identifier"
              • start: 210
              • end: 214
              • loc: {...}
                • start: {...}
                  • line: 9
                  • column: 10
                  }
                • end: {...}
                  • line: 9
                  • column: 14
                  }
                }
              • name: "flap"
              }
            • expression: false
            • generator: false
            • async: false
            • params: []
            • body: BlockStatement {...}
              • type: "BlockStatement"
              • start: 217
              • end: 235
              • loc: {...}
                • start: {...}
                  • line: 9
                  • column: 17
                  }
                • end: {...}
                  • line: 11
                  • column: 2
                  }
                }
              • body: [...] (1)
                • ExpressionStatement {...}
                  • type: "ExpressionStatement"
                  • start: 221
                  • end: 232
                  • loc: {...}
                    • start: {...}
                      • line: 10
                      • column: 2
                      }
                    • end: {...}
                      • line: 10
                      • column: 13
                      }
                    }
                  • expression: AssignmentExpression {...}
                    • type: "AssignmentExpression"
                    • start: 221
                    • end: 231
                    • loc: {...}
                      • start: {...}
                        • line: 10
                        • column: 2
                        }
                      • end: {...}
                        • line: 10
                        • column: 12
                        }
                      }
                    • operator: "+="
                    • left: Identifier {...}
                      • type: "Identifier"
                      • start: 221
                      • end: 226
                      • loc: {...}
                        • start: {...}
                          • line: 10
                          • column: 2
                          }
                        • end: {...}
                          • line: 10
                          • column: 7
                          }
                        }
                      • name: "count"
                      }
                    • right: Literal {...}
                      • type: "Literal"
                      • start: 230
                      • end: 231
                      • loc: {...}
                        • start: {...}
                          • line: 10
                          • column: 11
                          }
                        • end: {...}
                          • line: 10
                          • column: 12
                          }
                        }
                      • value: 1
                      • raw: "1"
                      }
                    }
                  }
                ]
              }
            }
          • ExpressionStatement {...}
            • type: "ExpressionStatement"
            • start: 238
            • end: 634
            • loc: {...}
              • start: {...}
                • line: 13
                • column: 1
                }
              • end: {...}
                • line: 23
                • column: 4
                }
              }
            • expression: CallExpression {...}
              • type: "CallExpression"
              • start: 238
              • end: 633
              • loc: {...}
                • start: {...}
                  • line: 13
                  • column: 1
                  }
                • end: {...}
                  • line: 23
                  • column: 3
                  }
                }
              • callee: Identifier {...}
                • type: "Identifier"
                • start: 238
                • end: 245
                • loc: {...}
                  • start: {...}
                    • line: 13
                    • column: 1
                    }
                  • end: {...}
                    • line: 13
                    • column: 8
                    }
                  }
                • name: "$effect"
                }
              • arguments: [...] (1)
                • ArrowFunctionExpression {...}
                  • type: "ArrowFunctionExpression"
                  • start: 246
                  • end: 632
                  • loc: {...}
                    • start: {...}
                      • line: 13
                      • column: 9
                      }
                    • end: {...}
                      • line: 23
                      • column: 2
                      }
                    }
                  • id: null
                  • expression: false
                  • generator: false
                  • async: false
                  • params: []
                  • body: BlockStatement {...}
                    • type: "BlockStatement"
                    • start: 252
                    • end: 632
                    • loc: {...}
                      • start: {...}
                        • line: 13
                        • column: 15
                        }
                      • end: {...}
                        • line: 23
                        • column: 2
                        }
                      }
                    • body: [...] (2)
                      • ExpressionStatement {...}
                        • type: "ExpressionStatement"
                        • start: 485
                        • end: 502
                        • loc: {...}
                          • start: {...}
                            • line: 18
                            • column: 2
                            }
                          • end: {...}
                            • line: 18
                            • column: 19
                            }
                          }
                        • expression: CallExpression {...}
                          • type: "CallExpression"
                          • start: 485
                          • end: 501
                          • loc: {...}
                            • start: {...}
                              • line: 18
                              • column: 2
                              }
                            • end: {...}
                              • line: 18
                              • column: 18
                              }
                            }
                          • callee: MemberExpression {...}
                            • type: "MemberExpression"
                            • start: 485
                            • end: 499
                            • loc: {...}
                              • start: {...}
                                • line: 18
                                • column: 2
                                }
                              • end: {...}
                                • line: 18
                                • column: 16
                                }
                              }
                            • object: Identifier {...}
                              • type: "Identifier"
                              • start: 485
                              • end: 493
                              • loc: {...}
                                • start: {...}
                                  • line: 18
                                  • column: 2
                                  }
                                • end: {...}
                                  • line: 18
                                  • column: 10
                                  }
                                }
                              • name: "$inspect"
                              }
                            • property: Identifier {...}
                              • type: "Identifier"
                              • start: 494
                              • end: 499
                              • loc: {...}
                                • start: {...}
                                  • line: 18
                                  • column: 11
                                  }
                                • end: {...}
                                  • line: 18
                                  • column: 16
                                  }
                                }
                              • name: "trace"
                              }
                            • computed: false
                            • optional: false
                            }
                          • arguments: []
                          • optional: false
                          }
                        • leadingComments: [...] (4)
                          • Line {...}
                            • type: "Line"
                            • value: " Because of this line, clicking the butterfly will cause information"
                            • start: 256
                            • end: 326
                            }
                          • Line {...}
                            • type: "Line"
                            • value: " to be logged to the console about which state changed to cause"
                            • start: 329
                            • end: 394
                            }
                          • Line {...}
                            • type: "Line"
                            • value: " the effect to re-run. (note: stack traces are better"
                            • start: 397
                            • end: 452
                            }
                          • Line {...}
                            • type: "Line"
                            • value: " outside the playground!)"
                            • start: 455
                            • end: 482
                            }
                          ]
                        }
                      • IfStatement {...}
                        • type: "IfStatement"
                        • start: 508
                        • end: 629
                        • loc: {...}
                          • start: {...}
                            • line: 20
                            • column: 2
                            }
                          • end: {...}
                            • line: 22
                            • column: 3
                            }
                          }
                        • test: BinaryExpression {...}
                          • type: "BinaryExpression"
                          • start: 512
                          • end: 525
                          • loc: {...}
                            • start: {...}
                              • line: 20
                              • column: 6
                              }
                            • end: {...}
                              • line: 20
                              • column: 19
                              }
                            }
                          • left: Identifier {...}
                            • type: "Identifier"
                            • start: 512
                            • end: 520
                            • loc: {...}
                              • start: {...}
                                • line: 20
                                • column: 6
                                }
                              • end: {...}
                                • line: 20
                                • column: 14
                                }
                              }
                            • name: "octupled"
                            }
                          • operator: ">"
                          • right: Literal {...}
                            • type: "Literal"
                            • start: 523
                            • end: 525
                            • loc: {...}
                              • start: {...}
                                • line: 20
                                • column: 17
                                }
                              • end: {...}
                                • line: 20
                                • column: 19
                                }
                              }
                            • value: 20
                            • raw: "20"
                            }
                          }
                        • consequent: BlockStatement {...}
                          • type: "BlockStatement"
                          • start: 527
                          • end: 629
                          • loc: {...}
                            • start: {...}
                              • line: 20
                              • column: 21
                              }
                            • end: {...}
                              • line: 22
                              • column: 3
                              }
                            }
                          • body: [...] (1)
                            • ExpressionStatement {...}
                              • type: "ExpressionStatement"
                              • start: 532
                              • end: 625
                              • loc: {...}
                                • start: {...}
                                  • line: 21
                                  • column: 3
                                  }
                                • end: {...}
                                  • line: 21
                                  • column: 96
                                  }
                                }
                              • expression: CallExpression {...}
                                • type: "CallExpression"
                                • start: 532
                                • end: 625
                                • loc: {...}
                                  • start: {...}
                                    • line: 21
                                    • column: 3
                                    }
                                  • end: {...}
                                    • line: 21
                                    • column: 96
                                    }
                                  }
                                • callee: Identifier {...}
                                  • type: "Identifier"
                                  • start: 532
                                  • end: 537
                                  • loc: {...}
                                    • start: {...}
                                      • line: 21
                                      • column: 3
                                      }
                                    • end: {...}
                                      • line: 21
                                      • column: 8
                                      }
                                    }
                                  • name: "alert"
                                  }
                                • arguments: [...] (1)
                                  • Literal {...}
                                    • type: "Literal"
                                    • start: 538
                                    • end: 624
                                    • loc: {...}
                                      • start: {...}
                                        • line: 21
                                        • column: 9
                                        }
                                      • end: {...}
                                        • line: 21
                                        • column: 95
                                        }
                                      }
                                    • value: "The flapping of the wings of a butterfly can be felt on the other side of the world."
                                    • raw: "'The flapping of the wings of a butterfly can be felt on the other side of the world.'"
                                    }
                                  ]
                                • optional: false
                                }
                              }
                            ]
                          }
                        • alternate: null
                        }
                      ]
                    }
                  }
                ]
              • optional: false
              }
            }
          ]
        • sourceType: "module"
        }
      • attributes: []
      }
    }
The AST is not public API and may change at any point in time