Modern JavaScript

const obj1 = {
  a: 'hello',
  say() {
    console.log(this.a, ...arguments);
  }
};

const obj2 = {
  a: 'buy'
};

// test
obj1.say.bind(obj2, 'friend', '!')();

The task is to implement a simple .bind polyfill for old browsers

• Functional way

function _bind(func, ctx) {
  var slice = Array.prototype.slice;
  
  if (arguments.length < 2) {
    return func.apply(ctx);
  }
  
  return func.apply(ctx, slice.call(arguments, 2));
}

// test
_bind(obj1.say, obj2, 'ttt', 'aaa');

• Extending Function.prototype

Function.prototype._bind = function(ctx) {
  const args = Array.prototype.slice.call(arguments, 1);
  const that = this;
  
  return function() {
    return that.apply(
      ctx,
      args.concat(Array.prototype.slice.call(arguments))
    );
  };
  
};

// test
obj1.say._bind(obj2, 'yyy', 'ccc')();