LibJS: Implement Function.prototype.bind()

Libraries/LibJS/Tests/Function.prototype.bind.js

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