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LibJS: Don't assume a this argument for function.prototype.bind

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Assuming we had at least one argument meant that the ...arg count would
underflow causing the bound function to have length 0 instead of the
given length when binding with no arguments.
This commit is contained in:
davidot 2022-08-15 21:25:23 +02:00 • committed by Linus Groh
parent c4f3d44be1
commit 9d05ca7b20
2 changed files with 14 additions and 1 deletions
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2
Userland/Libraries/LibJS/Runtime/FunctionPrototype.cpp
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@ -103,7 +103,7 @@ JS_DEFINE_NATIVE_FUNCTION(FunctionPrototype::bind)
auto* function = TRY(BoundFunction::create(global_object, target, this_argument, move(arguments)));
// 4. Let argCount be the number of elements in args.
auto arg_count = vm.argument_count() - 1;
auto arg_count = vm.argument_count() > 0 ? vm.argument_count() - 1 : 0;
// 5. Perform ? CopyNameAndLength(F, Target, "bound", argCount).
TRY(copy_name_and_length(global_object, *function, target, "bound"sv, arg_count));

13
Userland/Libraries/LibJS/Tests/builtins/Function/Function.prototype.bind.js
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@ -126,6 +126,19 @@ describe("bound function |this|", () => {
test("arrow functions cannot be bound", () => {
expect((() => this).bind("foo")()).toBe(globalThis);
});
test("length of original function is used for bound function", () => {
[0, 1, 2147483647, 2147483648, 2147483649].forEach(value => {
function emptyFunction() {}
Object.defineProperty(emptyFunction, "length", { value });
expect(emptyFunction.bind().length).toBe(value);
expect(emptyFunction.bind(null).length).toBe(value);
expect(emptyFunction.bind(null, 0).length).toBe(Math.max(0, value - 1));
expect(emptyFunction.bind(null, 0, 1, 2).length).toBe(Math.max(0, value - 3));
});
});
});
describe("bound function constructors", () => {