[Javascript] Write .call()
Function.apply.myCall = function (ctx, ...args) {
ctx = ctx === null || ctx === undefined ? globalThis : Object(ctx);
const fn = this;
const key = Sybmol("fn");
// we don't want user can see [Sybmol("key")] in Function prototype
// that's why we use Object.defineProperty to make it non-enumerable
Object.defineProperty(ctx, key, {
enumarable: false,
value: fn,
});
const r = ctx[key](...args);
return r;
};
function method(a, b) {
console.log("args:", a, b);
console.log("this:", this);
}
method.myCall(1, 2, 3); // this: [Number: 1]
method.myCall(null, 2, 3); // this: [global]
method.myCall(undefined, 2, 3); // this: [global]
method.myCall({}, 2, 3); // this: {}
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