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);

2. 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'));

3. 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)
   

4. 考察变量提升

   	var  foo = 1;
   	function fn(){
   		if(!foo){
   			var foo = 12;
   		}
   		console.log(foo);
   	}
   	fn();
   

5. 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)
   

6. 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);		
   

7. 逻辑与 逻辑或

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

8. 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)

9. 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：

1. 9
   10
   8 6
2. undefined
   false
   false
   true
   true
   true
3. a is not defined
4. 12
5. 3
   100
   undefined
6. 200
7. 2(逻辑与的优先级高于逻辑或)
8. 51 42
9. 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
10. window