手写bind函数

function fn(a, b, c, d) {
    console.log(this)
    console.log(a, b, c, d);
}
const cb = fn.bind({x: 100}, 1, 2, 3); // {x: 100}  1 2 3 undefined
cb();

// 手写bind
Function.prototype.myBind = function() {
    const fn = this;

    const arg = Array.prototype.slice.call(arguments);
    const _this = arg.shift();

    return function() {
        return fn.apply(_this, arg);
    }
}
const cb2 = fn.bind({x: 100}, 1, 2, 3); // {x: 100}  1 2 3 undefined
cb();