常用的数组方法

数组的方法有许多，但来来回回常用的也就那几种，特此记录，以备遗忘之需。

将数组合并成字符串

1. toString()
   直接把数组里的内容变成一个字符串
   var arr = [12,25,30,92]; var arr1 = arr.toString(); //arr1 = 12,25,30,92
2. join()
   以某种符号将数组内容串联成一个字符串
   var arr = [12,25,30,92]; var arr1 = arr.join('*'); //arr1 = 12*25*30*92

增加数组内容

1.push()
添加的内容按顺序放在数组最后面，并自动加长度

var arr = [12,25,30,92];
var arr1 = arr.push(51，65); //arr1 = [12,25,30,92,51,65]

2.unshift()
添加的内容按顺序放在数组的最前面，并自动增加长度

var arr = [12,25,30,92];
var arr1 = arr.unshift(51，65); //arr1 = [51,65,12,25,30,92]

取出数组内容

1.pop()
取出数组最后一个元素，并返回该值且在数组中消失

var arr = [12,25,30,92];
var poped = arr.pop();
 //arr = [12,25,30]   poped = 92

2.shift()
取出数组第一个元素，并返回该值且在数组中消失

var arr = [12,25,30,92];
var shifted = arr.shift();
 //arr = [25,30,92]   shifted = 12

3.slice(begin,end)
浅复制了数组内容,begin为开始复制的位置，end为结束复制的位置

var arr = [12,25,30,92];
var arr1 = arr.slice(1,3);
 //arr1 = [25,30,92]  

排序

排序的方法倒是只有一种，即sort（），但是分为升序和降序
1.升序
默认为升序

var arr = [12,0,25,30,92];
var arr1 = arr.sort();
//arr1 = [0,12,25,30,92]

还有另一种写法记得ab不能写反

var arr = [12,0,25,30,92];
var arr1 = arr.sort(functiion(a,b){
      return a-b;
});
//arr1 = [0,12,25,30,92]

2.降序

var arr = [12,0,25,30,92];
var arr1 = arr.sort(functiion(a,b){
      return b-a;
});
//arr1 = [92,30,25,12,0]

替换数组内容

splice(start,items,inplace);此方法从数组的start位置开始删除items个元素，并添加inplace元素

var myFish = ['angel', 'clown', 'mandarin', 'surgeon'];
// removes 0 elements from index 2, and inserts 'drum'
var removed = myFish.splice(2, 0, 'drum');
    // myFish is ['angel', 'clown', 'drum', 'mandarin', 'surgeon']
    // removed is [], no elements removed
// myFish is ['angel', 'clown', 'drum', 'mandarin', 'surgeon']
 // removes 1 element from index 3
removed = myFish.splice(3, 1);
    // myFish is ['angel', 'clown', 'drum', 'surgeon']
    // removed is ['mandarin']
// removes 1 element from index 2, and inserts 'trumpet'
removed = myFish.splice(2, 1, 'trumpet');
    // myFish is ['angel', 'clown', 'trumpet', 'surgeon']
    // removed is ['drum']
 // removes 2 elements from index 0, and inserts 'parrot', 'anemone' and 'blue'
removed = myFish.splice(0, 2, 'parrot', 'anemone', 'blue');
    // myFish is ['parrot', 'anemone', 'blue', 'trumpet', 'surgeon']
    // removed is ['angel', 'clown']
 // removes 2 elements from index 2
removed = myFish.splice(myFish.length -3, 2);
    // myFish is ['parrot', 'anemone', 'surgeon']
    // removed is ['blue', 'trumpet']

这一个引用了devdocs的demo

合并数组

concat();将两个数组合并成一个新数组，并返回该数组

var arr1 = [12,23,34];
var arr2 = ['hello','world'];
var arr3 =arr1.concat(arr2);
//arr3 = [12,23,34,'hello','world']

哪个数组使用了此方法，哪个就在前