[TOC]
## 数组排序
```
var a = [1, 54, 33, 556, 3334, 11]
```
### 1.冒泡排序
```
for (var i = 0; i < a.length; i++) {
for (var j = 0; j < a.length - 1; j++) {
if (a[i] < a[j]) {
var temp = a[i];
a[i] = a[j];
a[j] = temp
}
}
}
console.log(a)
```
### 2.js内置对象排序
```
var a = [1, 54, 33, 556, 3334, 11]
a.sort(function(i,j){
return i - j;
})
console.log(a)
```
## 去偶数合集
```
var temp = [ ]
for(var i = 0;i<a.length;i++){
if(a[i]%2==0){
temp.push(a[i]);
}
}
console.log(temp)
```
## 取最大，小值
```
<script>
var arr = [1,3,2,5,10,100,50];
var max = arr[0];
for(var i=0;i<arr.length;i++){
if(max<arr[i]){
max=arr[i]
}
}
console.log(max);
</script>
```
## 取反
```
console.log(a)
var temp = [];
for(var i = 0;i<a.length/2;i++){
var b = a[i]
a[i]= a[a.length-i-1]
a[a.length-i-1] = b;
}
console.log(a)
```
## 数组去重
~~~
1.新建一新数组，遍历旧数组，值不在新数组就push进该新数组中 !temp.includes(array[i])
2.根据数组下标去重 ：如果当前数组的第i项在当前数组中第一次出现的位置是i， 才存入数组；否则代表是重复的array.indexOf(array[i]) == i
3.遍历数组 ：元素0与右边的元素依次比较，若元素有重复，则结束元素0比较，将下一个元素1当做比较对象。直到没有重复再加入新数组，在进行下一次的比较（比较从加入数组的元素i开始）
if (array[i] === array[j]){
i++;
j = i;
}
~~~
### 1.判断值是否在数组中
```
var array = [1, 5, 7, 8, 5, 4, 3, 9, 7];
var newarr = []
for (var i = 0, j = array.length; i < j; i++) {
if (newarr.indexOf(array[i]) === -1) {
/* if (!newarr.includes(array[i]) ) { */
newarr.push(array[i]);
}
}
console.log(newarr)
```
### 2.判断当前值在数组中的下标是否为当前下标
```
var array = [1, 5, 7, 8, 5, 4, 3, 9, 7];
var newarr = []
for (var i = 0, j = array.length; i < j; i++) {
if (array.indexOf(array[i]) == i) {
newarr.push(array[i]);
}
}
console.log(newarr)
```
### 3.优化遍历法
```
var ar = [1, 5, 7, 8, 5, 4, 3, 9, 7];
var temp = [];
for (var i = 0; i < ar.length; i++) {
for (var j = i + 1; j < ar.length; j++) {
if (ar[i] === ar[j]) {
i++;
j = i;
}
}
temp.push(ar[i]);
}
console.log(temp)
```
## 数组复制
```
var a = [1,2,3,4]
var b = []
/* a.forEach(e => {
b.push(e)
}); */
/* b = [...a] */
/* b = b.concat(a) */
/* b.push(...a) */
/* b = a.slice(0) */
console.log(b)
```
## 数组遍历
```
a.forEach(element => {
b.push(element)
});
```
```
//可以用于object遍历
for (let i in a) {
b.push(a[i])
}
```
```
for (let i of a) {
b.push(i)
}
```
```
a.map(e=>{
b.push(e)
})
```
```
Array.from(a,e=>{
b.push(e)
})
console.log(b)
```
## 字符串去重成数组
> Set函数可以接受一个数组（或类似数组的对象）作为参数，用来初始化
> Set结构不会添加重复的值
> "abccaca" --> ["a", "b", "c"] --> "abc"
```
var e = [...new Set(a)].join("")
new Set(a) --->转化成对象去重
[...new Set(a)] --->将对象解构成数组
[...new Set(a)].join("") --->数组转化成字符串
```
