前端JS面试手写函数

1.用一个柯里化函数实现累加

// 柯里化函数
function currying(fn,length) {
    var length = length || fn.length;
    return function(...arg) {
        if(arg.length >= length) {
            return fn(...arg);
        } else {
            return currying(fn.bind(null,...arg),length-arg.length);
        }
    }
}
function $add(a1,a2,a3,a4) {
    return a1 + a2 + a3 + a4;
}
var add = currying($add,4);
console.log(add(1,2,3,4));
console.log(add(1,2)(3,4));
console.log(add(1)(2)(3,4));
console.log(add(1)(2)(3)(4));

2.实现一个bind函数

//myBind函数
Function.prototype.myBind = function (argThis,...arg) {
    const _Fn = this;
    return function() {
        const args = [...arg,...arguments];
        return _Fn.apply(argThis,args);
    }
}

var name = 'Nick'
function sayName() {
    return this.name
}
var obj = {
    name: 'Lily'
}
console.log(sayName())
var sayNamenew = sayName.myBind(obj);
console.log(sayNamenew())

3.实现一个new函数

//myNew函数
function Dog(name) {
    this.name = name;
    this.bar = function() {
        console.log(`my name is ${this.name}`)
    }
    // return this
}

function myNew(fn,...arg) {
    // let _Fn = new Object();
    // _Fn.__proto__ = fn.prototype;
    let _Fn = Object.create(fn.prototype);
    let result = fn.apply(_Fn,arg);
    return typeof result === 'object' ? result : _Fn;
}

var teddy = myNew(Dog,'Teddy');
console.log(teddy.name)
teddy.bar();