OOP - JavaScript Challenges

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

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OOP related challenges

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instanceof

/**
 * @param {any} obj
 * @param {target} target
 * @return {boolean}
 */

// One-line solution
function myInstanceOf(obj, fn) {
  return fn.prototype.isPrototypeOf(obj);
}

function myInstanceOf(obj, fn) {
  if (typeof obj !== "object" || obj === null) {
    return false;
  }

  if (typeof fn !== "function") {
    return false;
  }

  let proto = Object.getPrototypeOf(obj);

  while (proto) {
    if (proto === fn.prototype) {
      return true;
    }

    proto = Object.getPrototypeOf(proto);
  }

  return false;
}

// Usage example
class A {}
class B extends A {}
const b = new B();
console.log(myInstanceOf(b, B)); // => true
console.log(myInstanceOf(b, A)); // => true
console.log(myInstanceOf(b, Object)); // => true
function C() {}
console.log(myInstanceOf(b, C)); // => false
C.prototype = B.prototype;
console.log(myInstanceOf(b, C)); // => true
C.prototype = {};
console.log(myInstanceOf(b, C)); // => false

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new

/**
 * @param {Function} constructor
 * @param {any[]} args
 * `myNew(constructor, ...args)` should return the same as `new constructor(...args)`
 */

function myNew(constructor, ...args) {
  const obj = {};
  Object.setPrototypeOf(obj, constructor.prototype);

  const result = constructor.call(obj, ...args);

  if (typeof result !== "object" || result == null) {
    return obj;
  } else {
    return result;
  }
}

// Usage example
function Person(name) {
  this.name = name;
}
const person = myNew(Person, "Mike");
console.log(person); // => Person { name: 'Mike' }

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Reference

• 60. create your own new operator - BFE.dev
• 90. write your own instanceof - BFE.dev
• instanceof - MDN
• new - MDN
• Method chaining - Wikipedia.org
• 2726. Calculator with Method Chaining - LeetCode

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