前端常见面试题总结part2

今天总结了几道，感觉非常有意思的题，有感兴趣的可以看下,有疑问请留言~

(答案在最后)

1.

考察自执行函数的this指向

审题要细心

	var n = 2,

		obj = {

			n:2,

			fn:(function(n){

				n*=2;

				this.n+=2;

				console.log(this.n);

				console.log(window.n);

				return function(m){

					this.n*=2;

					console.log(m+(++n))

				}

			}(n)

		};

	var fn = obj.fn;

	fn(3);

	obj.fn(3)

	console.log(n,obj.n);

prototype：原型属性

_proto_: 原型链属性

hasOwnProperty:检测属性是否属于当前对象私有属性

	function Fn() {

            var n = 100;

            this.AA = function () { }

            this.BB = function () { }

        }

        Fn.prototype.AA = function () { }

        var f1 = new Fn();

        var f2 = new Fn;

        console.log(f1.n);

        console.log(f1.AA === f2.AA);

        console.log(f1.__proto__.AA === f2.AA)

        console.log(f1.__proto__.AA === f2.__proto__.AA)

        console.log(f1.__proto_.AA === Fn.prototype.AA)

        console.log(f1.hasOwnProperty('AA') === Fn.prototype.hasOwnProperty('AA'));

比较简单的一道题

	console.log(a);

	a = 20;

	function fn(){

		console.log(a)

		var a = 12;

	}

	fn();

	console.log(a)

考察变量提升

	var  foo = 1;

	function fn(){

		if(!foo){

			var foo = 12;

		}

		console.log(foo);

	}

	fn();

函数形参变量和arguments存在映射

函数默认返回undefined

	var a = 4;

	function test(x,y,a){

		console.log(a);

		arguments[2] = 100;

		console.log(a)

	}

	a = test(1,2,3);

	console.log(a)

函数形参变量和arguments映射建立在函数执行形参赋值的一刻

形参和实参一一对应，多出来的不建立映射

	function fn(x,y){

		var arg = arguments;

		arg[0] = 100;

		var y = 200;

		arg[1] = 300;

		console.log(y);

	}

	fn(20);

逻辑与逻辑或

	console.log(0||1&&2||0||3&&2||1)

还是考察this

	var num = 10;

	var obj = {num:20};

	obj.fn = (function(num){

		num = this.num + 10;

		this.num = num + 10;

		return function(){

			this.num += ++num;

		}

	})(num)

	var fn = obj.fn;

	fn();

	obj.fn();

	console.log(num,obj.num)

很长的一段

	function Fn(){

		this.x = 100;

		this.y = 200;

		this.getX = function(){

			console.log(this.x)

		}

	}

	Fn.prototype.getX = function(){

		console.log(this.x)

	}

	Fn.prototype.getY = function(){

		console.log(this.y)

	}

	var f1 = new Fn;

	var f2 = new Fn;

	console.log(f1.getX === f2.getX);

	console.log(f1.getY === f2.getY);

	console.log(f1.__proto__getY === Fn.prototype.getY);

	console.log(f1.__proto__.getX === f2.getX);

	console.log(f1.getX === Fn.prototype.getX);

	console.log(f1.constructor);

	console.log(Fn.prototype.__proto__.constructor);

	f1.getX();

	f1.__proto__.getX();

	f2.getY();

	Fn.prototype.getY();

10）还是this得问题（发现了好多this的题）

	var name = 'window';

	var Tom = {

		name:'Tom',

		show:function(){

			console.log(this.name)

		},

		wait:function(){

		var fun = this.show;

		fun();

		}

	}

	Tom.wait();

答案：

9

10

8 6
undefined

false

false

true

true

true
a is not defined
12
3

100

undefined
200
2(逻辑与的优先级高于逻辑或)
51 42
false

true

true

false

false

Fn

Object

100

undefined;this:f1.proto ,上面没有x，所以是undefined

200

undefined;this:Fn.prototype,上面没有y,所以是undefined
window

巴特西

前端常见面试题总结part2

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