手写 bind 函数

Function.prototype.bind2 = function(context) {
  const self = this;
  const args1 = [].slice.call(arguments, 1);
  const newFn = function() {
    const args2 = args1.concat([].slice.call(arguments));
    self.apply(this instanceof self ? this : context, args2);
  };
  newFn.prototype = self.prototype;
  return newFn;
};

function a(x = 0, y = 0) {
  console.log({ x, y });
}
const b = {};

a.bind(b)(1, 2);
a.bind2(b)(1, 2);

function c(name, hobby) {
  this.name = name;
  this.hobby = hobby;
}
const d = {};

const fn = c.bind(d, "Mike", "Eat");
console.log(new fn());
const fn2 = c.bind2(d, "Mike", "Eat");
console.log(new fn2());

Function.prototype.bind2 = function(context) {
  const _this = this;
  const args = [...arguments].slice(1);
  return function F() {
    if (this instanceof F) {
      return new _this(...args, ...arguments);
    }
    return _this.apply(context, args.concat(...arguments));
  };
};

function a(x = 0, y = 0) {
  console.log({ x, y });
}
const b = {};

a.bind(b)(1, 2);
a.bind2(b)(1, 2);

function c(name, hobby) {
  this.name = name;
  this.hobby = hobby;
}
const d = {};

const fn = c.bind(d);
console.log(new fn( "Mike", "Eat"));
const fn2 = c.bind2(d);
console.log(new fn2("Mike", "Eat"));