面试题

1.预编译

a=100;
function demo(e){
    arguments[0]=2;
    function e(){}
    console.log(e);//2
    if(a){
        var b=123;
    }
    a=10;
    var a;
    console.log(b);//undefined
    function c(){}
    var c;
    f=123;
    console.log(c);// function c(){}
    
}
var a;
demo(1);
console.log(a);//100
console.log(f);//123

2.包装类

原始值沒有属性和方法 ，通过包装类进行赋值，最后删除

var str='abc';
str+=1;
var test=typeof(str);

if(test.length==6){ 
    test.sign='123';//new String(test).sign='123'   delete
}else{
    test.sign='aaa';
}

console.log(test.sign); //undefined

3.实现下面的布局

方案一：justify-content: space-evenly; 兼容性不太好

方案二：利用伪元素

 

<div class="list"> 
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
</div>

.list {
    width: 100%;
    height: 200px;
    background: #000;
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.item {
    width: 100px;
    height: 100px;
    background: red;
}
.list:before {
    content: "";
    display: block;
}
.list:after {
    content: "";
    display: block;
}