* filter 不会改变原数组，不会对空数组进行检查
筛选符合条件项
var arr = ['10','12','23','44','42']
var newArr = arr.filter( (val) => val>30 )
console.log(newArr); // ["44", "42"]
去掉数组非真值（ undefined, null, false, ' ', 0 ）
var arr = [ '1', ' ', undefined, 2, null, '', 3, false, 0, true ];
var newArr = arr.filter( (val)=> val )
console.log(newArr); // ["1", " ", 2, 3, true]
// 空字符串不包含空格
数组去重
var arr = [ 1, 2, 3, 4, 1, 1, 2, 2, 3, 3, 4, 4, "a", "b", "c", "a", "b", "b" ];
var newArr = arr.filter( (val, index, arr) => arr.indexOf(val) === index );
console.log(newArr); // [1, 2, 3, 4, "a", "b", "c"]
根据数组对象中某个值进行查找
var arr = [
{ id:1, name:"abc", val:"aaa" },
{ id:2, name:"asd", val:"bbb" },
{ id:3, name:"qwe", val:"ccc" },
]
var newArr = arr.filter( (val) => val.id === 1 );
console.log(newArr); // [{id: 1, name: "abc", val: "aaa"}]