repo: github.com/alphardex/p…javascript
Python和JavaScript在筆者看來是很類似的語言,本文概括了JavaScript的各類tricks,相對於以前的Python版。java
兩篇文章都讀完,有沒有發現它們的目錄結構是一個樣的呢XDpython
let name = 'alphardex'
`Ore wa ${name} desu, ${4 * 6} sai, gakusei desu.`
// "Ore wa desu, 24 sai, gakusei desu."
複製代碼
// if(condition){
// fuck
// } else {
// shit
// }
(condition)? fuck: shit
複製代碼
let letters = ['咚', '噠', '呦', '!']
letters.join('')
// "咚噠呦!"
letters.reverse()
// ["!", "呦", "噠", "咚"]
let name = 'fujiwara chika'
name.split(' ')
// ["fujiwara", "chika"]
複製代碼
'fuck you'.includes('fuck')
// true
['bitch', 'whore'].includes('slut')
// false
'company' in {'title': 'Kaguya-sama: love is war', 'company': 'A1 Pictures'}
// true
複製代碼
函數的簡化寫法,配合map、filter、sort等實現函數式編程git
// function foo(parameters){
// return expression
// }
let foo = (parameters) => expression
複製代碼
let numbers = [1, 2, 3, 4, 5]
numbers.map(e=>e ** 2)
// [1, 4, 9, 16, 25]
複製代碼
let values = [null, undefined, NaN, 0, '', true, 'alphardex', 666]
values.filter(e=>e)
// [true, "alphardex", 666]
複製代碼
let numbers = [4, 2, 5, 1, 3]
numbers.sort((a, b)=>a-b) // 升序
// [1, 2, 3, 4, 5]
numbers.sort((a, b)=>b-a) // 降序
// [5, 4, 3, 2, 1]
複製代碼
求1到100的和github
[...Array(101).keys()].reduce((a, b)=>a+b)
// 5050
// 或者用lodash實現,寫法簡直跟Python如出一轍
// _.sum(_.range(101))
複製代碼
扁平化數組express
const flatten = (arr, depth=1) => arr.reduce((a, v)=>a.concat(depth>1 && Array.isArray(v)?flatten(v, depth-1):v), [])
let arr = [1, [2, 3, ['a', 'b', 4], 5], 6]
flatten(arr, 2)
// [1, 2, 3, "a", "b", 4, 5, 6]
// 或者用ES10新增的flat
// arr.flat(2)
複製代碼
let arr1 = ['kaguya', 'miyuki']
let arr2 = ['chika', 'ishigami']
[...arr1, ...arr2]
// ['kaguya', 'miyuki', 'chika', 'ishigami']
let obj1 = {'name': 'rimuru'}
let obj2 = {'kind': 'slime'}
{...obj1, ...obj2}
// {name: 'rimuru', kind: 'slime'}
複製代碼
// 打包
let foo = (...args) => console.log(args)
foo(1, 2)
// [1, 2]
// JS只能打包位置參數,沒法正確地打包關鍵詞參數
// foo(name='hayasaka', job='maid')
// ["hayasaka", "maid"] (keyword沒了)
// 解包
let divmod = (a, b) => [Math.floor(a/b), a % b]
let t = [10, 3]
let [quotient, remainder] = divmod(...t)
quotient
// 商:3
remainder
// 餘:1
複製代碼
只要函數中包含yield關鍵詞,這函數就是一個生成器函數編程
調用生成器函數時,會返回一個生成器對象數組
正如yield自己的意思(產出),對生成器對象調用next()會使其不斷產出值,直到無值才終止遍歷,done屬性變爲true數據結構
function* genHello() {
yield 'hello'
yield 'world'
}
g = genHello()
// genHello {<suspended>}
g.next()
// {value: "hello", done: false}
g.next()
// {value: "world", done: false}
g.next()
// {value: undefined, done: true}
複製代碼
若是生成器函數須要產出另外一個生成器生成的值,就要用到yield*函數式編程
function* chain(...iterables){
for(let it of iterables){
yield* it
}
}
let s = 'ABC'
let t = [...Array(3).keys()]
[...chain(s, t)]
// ["A", "B", "C", 0, 1, 2]
複製代碼
至關於Python的enumerate
let li = ['umaru', 'ebina', 'tachibana']
li.map((e, i)=>`${i+1}. ${e}`)
// ['1. umaru', '2. ebina', '3. tachibana']
複製代碼
push在末尾追加元素,concat在末尾鏈接元素
let li = [1, 2, 3]
li.push([4, 5])
li
// [1, 2, 3, [4, 5]]
li.concat([4, 5])
li
// [1, 2, 3, [4, 5], 4, 5]
複製代碼
every測試全部元素是否都知足於某條件,some則是測試部分元素是否知足於某條件
[1, 2, 3, 4, 5].every(e=>e<20)
// true
[1, 3, 4, 5].some(e=>e%2===0)
// true
複製代碼
至關於Python的zip
let subjects = ['nino', 'miku', 'itsuki']
let predicates = ['saikou', 'ore no yome', 'is sky']
subjects.map((e,i)=>`${e} ${predicates[i]}`)
// ["nino saikou", "miku ore no yome", "itsuki is sky"]
複製代碼
利用集合的互異性,同時此法還保留了原先的順序
let li = [3, 1, 2, 1, 3, 4, 5, 6]
[...new Set(li)]
// [3, 1, 2, 4, 5, 6]
複製代碼
最典型的例子就是2數交換
let [a, b] = [b, a]
複製代碼
用rest運算符能夠獲取剩餘的元素
let [first, ...rest] = [1, 2, 3, 4]
first
// 1
rest
// [2, 3, 4]
複製代碼
let obj = {'name': 'sekiro', 'hobby': 'blacksmithing', 'tendency': 'death'}
Object.keys(obj)
// ["name", "hobby", "tendency"]
Object.values(obj)
// ["sekiro", "blacksmithing", "death"]
Object.entries(obj).map(([key, value])=>`${key}: ${value}`)
// ["name: sekiro", "hobby: blacksmithing", "tendency: death"]
複製代碼
let data = [{'rank': 2, 'author': 'beta'}, {'rank': 1, 'author': 'alpha'}]
data.sort((a, b)=>a.rank - b.rank)
// [{'rank': 1, 'author': 'alpha'}, {'rank': 2, 'author': 'beta'}]
複製代碼
let obj = {'name': 'sakurajima mai', 'suit': 'bunny girl'}
Object.fromEntries(Object.entries(obj).map(([key, value])=>[value, key]))
// {sakurajima mai: "name", bunny girl: "suit"}
// 或者用lodash實現
// _.invert(obj)
複製代碼
若是鍵不在字典中,返回一個默認值,相似Python的dict.get
let obj = {'name': 'okabe rintaro', 'motto': 'elpsycongroo'}
obj.job || 'mad scientist'
// mad scientist
複製代碼
若是鍵不在字典中,將會添加它並設置一個默認值,相似Python的dict.setdefault
let obj = {'name': 'okabe rintaro', 'motto': 'elpsycongroo'}
obj.job = obj.job || 'mad scientist'
// "mad scientist"
obj
// {name: "okabe rintaro", motto: "elpsycongroo", job: "mad scientist"}
複製代碼
待整理