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LibJS: Implement Function.prototype.bind()
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10 changed files with 317 additions and 6 deletions
112
Libraries/LibJS/Tests/Function.prototype.bind.js
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112
Libraries/LibJS/Tests/Function.prototype.bind.js
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load("test-common.js");
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try {
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assert(Function.prototype.bind.length === 1);
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var charAt = String.prototype.charAt.bind("bar");
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assert(charAt(0) + charAt(1) + charAt(2) === "bar");
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function getB() {
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return this.toUpperCase().charAt(0);
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}
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assert(getB.bind("bar")() === "B");
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function sum(a, b, c) {
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return a + b + c;
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}
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// Arguments should be able to be bound to a function.
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var boundSum = sum.bind(null, 10, 5);
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assert(isNaN(boundSum()));
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assert(boundSum(5) === 20);
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assert(boundSum(5, 6, 7) === 20);
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// Arguments should be appended to a BoundFunction's bound arguments.
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assert(boundSum.bind(null, 5)() === 20);
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// A BoundFunction's length property should be adjusted based on the number
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// of bound arguments.
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assert(sum.length === 3);
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assert(boundSum.length === 1);
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assert(boundSum.bind(null, 5).length === 0);
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assert(boundSum.bind(null, 5, 6, 7, 8).length === 0);
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function identity() {
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return this;
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}
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// It should capture the global object if the |this| value is null or undefined.
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assert(identity.bind()() === globalThis);
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assert(identity.bind(null)() === globalThis);
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assert(identity.bind(undefined)() === globalThis);
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function Foo() {
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assert(identity.bind()() === globalThis);
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assert(identity.bind(this)() === this);
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}
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new Foo();
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// Primitive |this| values should be converted to objects.
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assert(identity.bind("foo")() instanceof String);
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assert(identity.bind(123)() instanceof Number);
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assert(identity.bind(true)() instanceof Boolean);
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// It should retain |this| values passed to it.
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var obj = { foo: "bar" };
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assert(identity.bind(obj)() === obj);
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// The bound |this| can not be changed once set
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assert(identity.bind("foo").bind(123)() instanceof String);
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// The bound |this| value should have no effect on a constructor.
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function Bar() {
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this.x = 3;
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this.y = 4;
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}
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Bar.prototype.baz = "baz";
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var BoundBar = Bar.bind({ u: 5, v: 6 });
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var bar = new BoundBar();
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assert(bar.x === 3);
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assert(bar.y === 4);
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assert(typeof bar.u === "undefined");
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assert(typeof bar.v === "undefined");
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// Objects constructed from BoundFunctions should retain the prototype of the original function.
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assert(bar.baz === "baz");
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// BoundFunctions should not have a prototype property.
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assert(typeof BoundBar.prototype === "undefined");
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// Function.prototype.bind should not accept non-function values.
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assertThrowsError(() => {
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Function.prototype.bind.call("foo");
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}, {
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error: TypeError,
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message: "Not a Function object"
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});
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// A constructor's arguments should be able to be bound.
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var Make5 = Number.bind(null, 5);
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assert(Make5() === 5);
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assert(new Make5().valueOf() === 5);
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// FIXME: Uncomment me when strict mode is implemented
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// function strictIdentity() {
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// return this;
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// }
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// assert(strictIdentity.bind()() === undefined);
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// assert(strictIdentity.bind(null)() === null);
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// assert(strictIdentity.bind(undefined)() === undefined);
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// })();
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// FIXME: Uncomment me when arrow functions have the correct |this| value.
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// // Arrow functions can not have their |this| value set.
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// assert((() => this).bind("foo")() === globalThis)
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console.log("PASS");
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} catch (e) {
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console.log("FAIL: " + e);
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}
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