SOURCE

//基本数据类型
let a = 'test';
let b = a;
b = 'ceshi1';
console.log(a, b);

//引用数据类型
let arr = ['1', '2', 3]
let arr1 = arr;
arr1.push(4);
console.log(arr, arr1)

let newarr = arr.forEach(function(item){
    return item+1;
    console.log(item)
})
//forEach is void, can not return anything
console.log(newarr)

<span class="spanwrap">
    1233333
    <div>123123</div>
</span>

.spanwrap{
    padding-left: 50px;
}
.spanwrap div{
    width: 50%;
    height: 200px;
    border: 1px solid red;
}