Function prototype - JavaScript Challenges

You can find all the code in this post at repo Github.

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Function prototype related challenges

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Function.prototype.call()

/**
 * @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

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Function.prototype.apply()

/**
 * @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

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Function.prototype.bind()

/**
 * @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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Reference

• GreatFrontEnd
• 61. create your own Function.prototype.call - BFE.dev
• Function.prototype.call() - MDN
• Function.prototype.apply() - MDN
• Function.prototype.bind() - MDN