[Webkit-unassigned] [Bug 152028] New: Unexpected exception assigning to this._property inside arrow function

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=152028

            Bug ID: 152028
           Summary: Unexpected exception assigning to this._property
                    inside arrow function
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: joepeck at webkit.org
                CC: bburg at apple.com, ggaren at apple.com,
                    gskachkov at gmail.com, mattbaker at apple.com,
                    sbarati at apple.com
            Blocks: 140855

* SUMMARY
Unexpected exception assigning to this._property inside arrow function.

"TypeError: Attempted to assign to readonly property." is thrown when attempting to do something like "this._property = value" inside of an arrow function. I do not expect this to happen. "this" itself might be readonly, but "this._property" should writeable.

* TEST
<script>
"use strict";
class Logger {
    constructor() {
        this._id = undefined;
    }
    scheduleLog() {
        if (this._id) return;
        this._id = requestAnimationFrame(() => {
            this._id = undefined;
            console.log("Logged!");
        });
    }
}

var logger = new Logger;
logger.scheduleLog();
</script>

* STEPS TO REPRODUCE
1. Load the test case above
  => Unexpected exception

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