POP 删除最后一项
删除最后一项,并返回删除元素的值；如果数组为空则返回undefine
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var a = [1,2,3,4,5];
a.pop();//a：[1,4]
a.pop();//a：[1,3]
a.pop();//a：[1,2]
shift 删除第一项
删除原数组第一项，并返回删除元素的值；如果数组为空则返回undefine
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var a = [1,5];
a.shift(); //a：[2,5]
a.shift(); //a：[3,5]
push 增加到最后
并返回新数组长度；
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var a = [1,5];
a.push(6);//[1,5,6]
aa.push('xx');//[1,6,"xx"] 返回长度7
a.push('yy');//[1,"xx","yy"] 返回长度8
unshift增加到最前
并返回新数组长度；
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var a = [1,5];
a.unshift();//[1,5]
a.unshift("cc");//["cc",1,5] 返回长度6
a.unshift("aaa");//["aaa","cc",5] 返回长度7
reverse 数组翻转
并返回翻转后的原数组，原数组翻转了
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var a = [1,5];
a.reverse()//a：[5,1] 返回[5,1]
join数组转成字符串
并返回字符串，原数组木变
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var a = [1,5];
var b=a.join('||');//b:"1||2||3||4||5" a:[1,5]
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var a = ['a','b','c','d','e'];
a.indexOf('a');//0
a.indexOf(a);//-1
a.indexOf('f');//-1
a.indexOf('e');//4
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var a = ['a','e'];
a.slice(1,3);//["b","c"] a:['a','e']
a.slice(0,4);//["a","b","c","d"]
a.slice(3,4);//["d"]
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/*参数是2个*/
//第一参数是索引（从0开始），第二是长度
var a = ['a','e'];
a.splice(0,2);//["a","b"] a:["c","d","e"]
a.splice(0,2);//["c","d"] a:["e"]
var a = ['a',1);//["a"] a:["b","e"] 同shift前
删除
var a = ['a','e']
a.splice(a.length-1,1)l//["e"] a:["a","d"] 同pop前
删除
/*参数大于2个*/
//splice(start,deleteCount,val1,val2,...)：从start位置开始
删除deleteCount项，并从该位置起插入val1,...
var a = ['a','e'];
a.splice(3,10,21,238,99);//["d"] a:["a",99,"e"]
var a = ['a','e'];
a.splice(a.length,100000000,88)//返回 [] 从最后元素后面的元素，
截取长度任意个，肯定是空 a：["a","e",88] 同push后
增加
var a = ['a','e'];
a.splice(0,88,99)//返回 [] 从第
一个元素，
截取长度0个 肯定是空 a:[88,"a","e"] 同unshift前
增加
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var a = ['a','e'];
a.concat([88,99]);//["a",99] a:["a","e"]
var b= [9999,10000]
a.concat(b);// ["a",9999,10000] a:["a","e"]
