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/** * @param {any} thisArg * @param {...*} argArray * @return {any} */ Function.prototype.myCall = function (thisArg, ...argArray) { const sym = Symbol(); const wrapperObj = Object(thisArg); Object.defineProperty(wrapperObj, sym, { enumerable: false, value: this, }); return wrapperObj[sym](...argArray); }; // Usage example function multiplyAge(multiplier = 1) { return this.age * multiplier; } const mary = { age: 21, }; const john = { age: 42, }; console.log(multiplyAge.myCall(mary)); // 21 console.log(multiplyAge.myCall(john, 2)); // 84
/** * @param thisArg The object to be used as the this object. * @param argArray A set of arguments to be passed to the function. * @return {any} */ Function.prototype.myApply = function (thisArg, argArray = []) { const sym = Symbol(); const wrapperObj = Object(thisArg); Object.defineProperty(wrapperObj, sym, { enumerable: false, value: this, }); return wrapperObj[sym](...argArray); }; // Usage example function multiplyAge(multiplier = 1) { return this.age * multiplier; } const mary = { age: 21, }; const john = { age: 42, }; console.log(multiplyAge.myApply(mary)); // 21 console.log(multiplyAge.myApply(john, [2])); // 84
/** * @param {any} thisArg * @param {...*} argArray * @return {Function} */ Function.prototype.myBind = function (thisArg, ...argArray) { const sym = Symbol(); const wrapperObj = Object(thisArg); Object.defineProperty(wrapperObj, sym, { enumerable: false, value: this, }); return function (...args) { return wrapperObj[sym](...argArray, ...args); }; }; // Usage example const john = { age: 42, getAge: function () { return this.age; }, }; const unboundGetAge = john.getAge; console.log(unboundGetAge()); // undefined const boundGetAge = john.getAge.myBind(john); console.log(boundGetAge()); // 42 const jack = { age: 21, getAge: function () { return this.age; }, }; // For multiple `.bind()` chaining, only the first one would work const boundJohnGetAge = john.getAge.myBind(john).myBind(jack); console.log(boundGetAge()); // 42
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