filter函數可以看成是一個過濾函數,返回符合條件的元素的數組
filter需要在循環的時候判斷一下是true還是false,是true纔會返回這個元素;
let arr1 = [1,2,3];
let arr2 = arr1.filter((value,key,arr) => {
console.log(value) // 1,2,3
console.log(key) // 0,1,2
console.log(arr) // [1,2,3]
return value >= 3 ? false : true;
})
console.log(arr1); // [ 1, 2, 3 ]
console.log(arr2); // [ 1, 2 ]
1.filter() 過濾不符合項
let arr = [1,2,3]
let newArr = arr.filter(item => item>=3)
console.log(newArr)
2.filter() 去掉空字符串、undefined、null
let arr = ['','1','2',undefined,'3.jpg',undefined]
let newArr = arr.filter(item => item)
console.log(newArr)
3.filter() 數組去重
let arr = [1, 2, 2, 3, 4, 5, 5, 6];
let newArr = arr.filter((x, index,self)=>self.indexOf(x)===index)
console.log(newArr)
去重推薦使用 set()方法
let arr = [1, 2, 2, 3, 4, 5, 5, 6];
let newArr =Array.from(new Set(arr))
console.log(newArr)
4.filter() 篩選數組對象
let arr = [
{a:'蘋果',b:'麪包',c:'吃'},
{a:'香蕉',b:'麪包',c:'不吃'},
{a:'香蕉',b:'蘋果',c:'吃'},
{a:'蘋果',b:'香蕉',c:'不吃'},
]
console.log(arr.filter(item => item.a=== '蘋果' ))//[{a:'蘋果',b:'麪包',c:'吃'},{a:'蘋果',b:'香蕉',c:'不吃'}]
let a = '蘋果'; //篩選參數a
let b = '麪包'; //篩選參數b
let c = '' //篩選參數c
let arr = [
{a:'蘋果',b:'麪包',c:'吃'},
{a:'香蕉',b:'麪包',c:'不吃'},
{a:'香蕉',b:'蘋果',c:'吃'},
{a:'蘋果',b:'香蕉',c:'不吃'},
];
arr = arr.filter(item => (a?item.a === a : true) && (b?item.b === b : true) && (c?item.c === c : true))
console.log(arr) // 篩選結果: [{a:'蘋果',b:'麪包',c:'吃'}]