callBindApply.js

// Explicitly binding

let user = { name: "sudhakar" };

function printName(age) {
  console.log(this.name, +age);
}

// as here this refers to window object.

// For every function call apply bind is available

printName();

printName.call(user, 24); // here first praram is obj and next params are argumnents of function

printName.apply(user, [24]); // apply is same as call where in call args are passed individudally but in apply as array

const bindFunc = printName.bind(user); // bind will create new function with binding the object with function

bindFunc(24);

// call polyfill

Function.prototype.myCall = function (context = {}, ...args) {
  if (typeof this !== "function") {
    throw new Error("it should be function");
  }

  context.fn = this;
  context.fn(...args);
};

printName.myCall(user, 24);

// apply polyfill

Function.prototype.myApply = function (context = {}, [args]) {
  if (typeof this !== "function") {
    throw new Error("it should be function");
  }

  context.fn = this;
  context.fn([args]);
};

printName.myApply(user, [24]);

// bind polyfill

Function.prototype.myBind = function (context = {}, ...args) {
  if (typeof context !== "function") {
    throw new Error("it should be a function");
  }

  return function (...newArgs) {
    context.fn = this;
    context.fn(...args, ...newArgs);
  };
};