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LibJS: let variables are not captured correctly #23552

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tcl3 opened this issue Mar 11, 2024 · 1 comment
Open

LibJS: let variables are not captured correctly #23552

tcl3 opened this issue Mar 11, 2024 · 1 comment
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bug Something isn't working has-repro We have a way to reproduce this bug.

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@tcl3
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tcl3 commented Mar 11, 2024

When a let variable is captured by a function, it's value at the time it was captured should be used. Currently, Ladybird behaves as if a var variable was being captured.

Example:

<!DOCTYPE html>
<script>
    let result = "";
    let functionList = [];
    for (let i = 0; i < 9; i++) {
      functionList.push(function() {
          return i;
      });
    }
    for (let i = 0; i < functionList.length; i++) {
        result += functionList[i]();
    }
    // Output in Ladybird is: 999999999.
    // Output should be: 012345678.
    console.log(result); 
</script>

I initially spotted this while working on #23544, looking at this WPT subtest.
@tcl3 tcl3 added bug Something isn't working has-repro We have a way to reproduce this bug. labels Mar 11, 2024
@tcl3 tcl3 mentioned this issue Mar 11, 2024
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@Lubrsi
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Lubrsi commented Mar 11, 2024

This could potentially be us missing CreatePerIterationEnvironment: https://tc39.es/ecma262/multipage/ecmascript-language-statements-and-declarations.html#sec-createperiterationenvironment

For example, logging result in the function shows that result is captured by reference instead of by value:

    let result = "";
    let functionList = [];
    for (let i = 0; i < 9; i++) {
      result += i;
      functionList.push(function() {
          console.log(result);
          return i;
      });
    }
    for (let i = 0; i < functionList.length; i++) {
        result += functionList[i]();
    }
    console.log(result);

Chrome:
image
Ladybird:
image

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