ES5/ES6/ES7/ES8
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數組常用方法
Array.indexOf()
:得到值在數組中的第一個下標,沒找到返回-1
使用示例:找到數組中是否包含某個元素,返回Boolean值
return ['春','夏','秋','冬'].indexOf('夏') !== '-1'
Array.join()
: 把數組轉成需要的字符串
const arr = [1, 2, 3, 4, 5, 6, 7] const str1 = arr.join() // 1,2,3,4,5,6,7 const str2 = arr.join('-') // 1-2-3-4-5-6-7
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Array.slice(start,end)
const sliceArr = arr.slice(3) // [4, 5, 6, 7]
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Array.some()
const isBoolean = arr.some((item, index) => item > 5) // true
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Array.filter()
const filterArr = arr.filter(item => {return item > 5}) // [6, 7]
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Array.forEach()
arr.forEach(function(item, index, a) { console.log(item, index, a) console.log(this) // [1, 2, 3, 4, 5, 6, 7] }, arr) arr.forEach( item => { item*3 console.log(this) // window }, arr)
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Array.map()
const mapArr = arr.map(item => item*3) // [3, 6, 9, 12, 15, 18, 21]
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Array.reduce()
const reduceArr = arr.reduce((prev, item, index) => prev + item) // 28
如果我們需要實現這樣一個對象
{ a: 1, b: 2, c: 3 ...}
const newArr = 'a,b,c,d,e,f'.split(',').reduce((acc, cur, idx) => { let o = {} if (Object.prototype.toString.call(acc) !== '[object Object]') { o[cur] = idx } else { let newO = {} newO[cur] = idx o = { ...acc, ...newO, } } return o }, 'a') console.log(newArr) // {a: 0, b: 1, c: 2, d: 3, e: 4, f: 5}
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Array.flat(depth)
arr.push([3, 4, 5, 9]) // [1, 2, 3, 4, 5, 6, 7, [3, 4, 5, 9]] // depth: 1,2, ... , Infinity const flatArr = arr.flat(1) // [1, 2, 3, 4, 5, 6, 7, 3, 4, 5, 9]
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Array.splice(index, howmany)
const spliceArr = arr.splice(1,1) // [2, 3, 4, 5, 6] 改變原數組 console.log(spliceArr) console.log(arr) // [1, 7]
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Array.find()
const findArr = [1, 2, 3, 4].find(item => item > 2 ) // 3