Function.prototype.softBind = function(obj, ...rest) {
    const fn = this
    const bound = function(...args) {
      const o = !this || this === (window || global) ? obj : this
      return fn.apply(o, [...rest, ...args])
    }

    bound.prototype = Object.create(fn.prototype)
    return bound
  }

let obj = {name: "obj"};
obj2 = {name: "obj2"};
obj3 = {name: "obj3"};

let fooBJ = foo.softBind(obj);
fooBJ();  // name: obj   这个时候软绑定已经生效了，this绑定到obj上
obj2.foo = foo.softBind(obj);
obj2.foo(); //name: obj2   这里已经的this隐式绑定到obj2上了
fooBJ.call(obj3); // name: obj3  这里this被硬绑定到obj3上了
setTimeout(obj2.foo, 100); // name: obj  软绑定了最初的obj

function person(a, b, c, d, e) {
    console.log(this.name, a + b + c);
    console.log(d,e);
}

const yeti = {
    name: 'yeti'
}

// 实现一个bind
Function.prototype.newmyBind = function (obj, ...args) {
    const that = this
    return function (...rest) {  //返回一个修改好this的函数
        // ...rest来自返回函数传入的参数  ...args是调用Bind时传入的参数
        that.call(obj, ...args, ...rest)
    }

}

const resBind = person.newmyBind(yeti, 1, 2, 6) //1 2 6 就是...args
resBind(5, 6)   //传入...rest