``` var d=[1,2];//[1,2] var a={ a:'1', b:'2' }; console.log(a);//{a:1,b:2} var b=new Array; b['a']=1; b['c']=2; console.log(b);//[a:1.c:2] //删除 delete b['a']; ``` 尾部追加 ``` arr =[{'num':1},{'num':2},{'num':3}]; newArr = arr.push({'num':4}) console.log(arr) ``` 头部追加 ``` arr =[{'num':3},{'num':4},{'num':5}]; newArr = arr.unshift({'num':2}) console.log(arr) ```