js常规数组操作，es6filter（）数组过滤⽅法总结 1 Array.every(x=>x)是每⼀个都要满⾜
2
3 Array.some(x=>x)是有⼀个满⾜。
4
5 Array.find（findIndex)，返回符合条件的第⼀个值。
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7 Array.filter（过滤成新的数组）
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9数组的⽅法分为两类
10
11 1）改变原数组
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13 push,pop,shift,unshift,sort,reverse,splice
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15 2）不改变原数组fliter,concat,join-->
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17 split，toStringpush：从数组最后⼀位开始加数据
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19 pop：把数组最后⼀位剪切
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21 shift：在数组最前⼀位剪切
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23 unshift：在数组最前⼀位加数
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25 reverse：把原数组逆转
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27 splice:arr.splice(从第⼏位开始，截取多少长度，在切⼝处添加新数据)
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29 concat ：连接join：返回字符串
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31 slice：截取arr.slice(从该为开始截取，截取到该为)
⽰例
1.创建⼀个数组，判断数组中是否存在某个值
var newarr = [
{ num: 1, val: 'ceshi', flag: 'aa' },
{ num: 2, val: 'ceshi2', flag: 'aa2' }
]
console.log(newarr.filter(item => item.num===2 ))
2.也可以通过上⾯⽅法过滤掉num为2的留下num为1的
var newarr = [
{ num: 1, val: 'ceshi', flag: 'aa' },
{ num: 2, val: 'ceshi2', flag: 'aa2' }
]
console.log(newarr.filter(item => item.num!=2 ))
3.去掉空数组空字符串、undefined、null
var arr = ['1','2',undefined, '3.jpg',undefined]
var newArr = arr.filter(item => item)
console.log(newArr)
var arr = ['1','2',null, '3.jpg',null]
var newArr = arr.filter(item => item)
console.log(newArr)
>//空字符串⾥⾯不能包含空格
var arr = ['1','2','', '3.jpg','']
var newArr = arr.filter(item => item)
console.log(newArr)
4.去掉数组中不符合项
var arr = [20,30,50, 96,50]
var newArr = arr.filter(item => item>40)
console.log(newArr)
5.过滤不符合项
var arr = ['10','12','23','44','42']
var newArr = arr.filter(item => item.indexOf('2')<0)
console.log(newArr)
6.数组去重
var arr = [1, 2, 2, 3, 4, 5, 5, 6, 7, 7,8,8,0,8,6,3,4,56,2];
var arr2 = arr.filter((x, index,self)=>self.indexOf(x)===index)
filter过滤对象数组
console.log(arr2); //[1, 2, 3, 4, 5, 6, 7, 8, 0, 56]
/*
7  有⼀个对象数组 a ，将a数中对象某个属性的值存储到B数组中
*/
var porducts = [
{name:"cucumber",type:"vegetable"},
{name:"banana",type:"fruit"},
{name:"celery",type:"vegetable"},
{name:"orange",type:"fruit"},
];
// es5
var filteredProducts = [];
for(var i = 0;i < porducts.length; i ++){
if(porducts[i].type === "fruit"){
// 如果条件满⾜就把当前的值推⼊
filteredProducts.push(porducts[i])
}
}
// console.log(filteredProducts)//0: {name: "banana", type: "fruit"}1: {name: "orange", type: "fruit"}length: 2__proto__: Array(0)
// ES6
var filter2 = porducts.filter(function(porduct){//对porducts数组对象过滤如果pe === "fruit"就return出去，再⽤⼀个变量接住
pe === "fruit"
})
console.log(filter2)
/*
需求⼆
8 有⼀个对象数组A，过滤掉不满⾜以下条件对象
条件：蔬菜数量⼤于0 价格⼩于10
*/
var products = [
{name:"cucumber",type:"vegetable",quantity:0,price:1},
{name:"banana",type:"fruit",quantity:10,price:16},
{name:"celery",type:"vegetable",quantity:30,price:8},
{name:"orange",type:"fruit",quantity:3,price:6},
];
products = products.filter(function(product){
pe === "vegetable"
&& product.quantity > 0
&& product.price < 10
})
console.log(products)//0: {name: "celery", type: "vegetable", quantity: 30, price: 8}name: "celery"price: 8quantity: 30type: "vegetable"__proto__: Objectlength: 1__proto__: Array(0) /*
需求三:
9 有两个数组A,B，根据A中的ID值 ，过滤掉B数组不符合的数据
*/
var post = {id:4,title:"javascript"};
var comments = [
{postId:4,content:'Angular4'},
{postId:2,content:'VUE.js'},
{postId:3,content:'Node.js'},
{postId:4,content:'React.js'},
];
function commentsForPost(post,comments){
return comments.filter(function(comment){
return comment.postId === post.id;
})
}
console.log(commentsForPost(post,comments))
// 0: {postId: 4, content: "Angular4"}1: {postId: 4, content: "React.js"}length: 2__

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