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<body><span class="vcard"><a class="email" href="mailto:darin@apple.com" title="Darin Adler <darin@apple.com>"> <span class="fn">Darin Adler</span></a>
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<a class="bz_bug_link
bz_status_NEW "
title="NEW - [JSC] add missing RequireObjectCoercible() step in destructuring"
href="https://bugs.webkit.org/show_bug.cgi?id=151596">bug 151596</a>
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<td style="text-align:right;">Attachment #266145 Flags</td>
<td>review?
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<td>review+
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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - [JSC] add missing RequireObjectCoercible() step in destructuring"
href="https://bugs.webkit.org/show_bug.cgi?id=151596#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - [JSC] add missing RequireObjectCoercible() step in destructuring"
href="https://bugs.webkit.org/show_bug.cgi?id=151596">bug 151596</a>
from <span class="vcard"><a class="email" href="mailto:darin@apple.com" title="Darin Adler <darin@apple.com>"> <span class="fn">Darin Adler</span></a>
</span></b>
<pre>Comment on <span class=""><a href="attachment.cgi?id=266145&action=diff" name="attach_266145" title="[JSC] add missing RequireObjectCoercible() step in destructuring">attachment 266145</a> <a href="attachment.cgi?id=266145&action=edit" title="[JSC] add missing RequireObjectCoercible() step in destructuring">[details]</a></span>
[JSC] add missing RequireObjectCoercible() step in destructuring
View in context: <a href="https://bugs.webkit.org/attachment.cgi?id=266145&action=review">https://bugs.webkit.org/attachment.cgi?id=266145&action=review</a>
<span class="quote">> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:3849
> + emitJumpIfFalse(emitIsUndefined(newTemporary(), value), isNotUndefined.get());</span >
We can save a branch in the normal expected fast path by doing the other check first; then do emitIsUndefined only the failure case to chose which error to throw; undefined is equal to null from the point of view of op_eq_null.
<span class="quote">> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:3853
> + emitJumpIfFalse(emitUnaryOp(op_eq_null, newTemporary(), value), target.get());</span >
Unfortunately this emits the “masquerades as null” checking code, so it’s unnecessarily slow. Here we are not literally checking == null so we don’t want that extra logic; it just slows us down. One way to do this would be to add a new op_is_undefined_or_null that doesn’t bother with the masquerading logic. Or op_is_object_coercible.
<span class="quote">> Source/JavaScriptCore/tests/stress/destructuring-assignment-require-object-coercible.js:15
> +testTypeError(`({ } = null)`, "TypeError: null is not an object");</span >
Would be much better to check all the other types here too, an object, number, boolean, string, and especially a “masquerades as null” value, making sure that they do not throw a type error.</pre>
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