17个你可能还不知道 JS 技巧！

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1.三元运算符

---

新手

let hungry = true;

let eat;

if (hungry == true) {

eat = ‘yes’;

} else {

eat = ‘no’;

}

老手

let hungry = true;

let eat = hungry == true ? ‘yes’ : ‘no’;

2.数字转字符串/字符串转数字

---

新手

let num = 15;

let s = num.toString(); // number to string

let n = Number(s); // string to number

老手

let num = 15;

let s = num + “”; // 数字转字符串

let n = +s; // 字符串转数字

3.填充数组

---

新手

for(let i=0; i < arraySize; i++){

filledArray[i] {‘hello’ : ‘goodbye’};

}

老手

let filledArray = new Array(arraysize).fill(null).map(()=> ({‘hello’ : ‘goodbye’}));

4.对象的动态属性

---

新手

let dynamic = “value”;

let user = {

id: 1,

};

user[dynamic] = “other value”;

老手

let dynamic = “value”;

let user = {

id: 1,

[dynamic] : “other value”

};

5.删除重复项

---

新手

let array = [100, 23, 23, 23, 23, 67, 45];

let outputArray = [];

let flag = false;

for (j = 0; < array.length; j++) {

for (k = 0; k < outputArray.length; k++) {

if (array[j] == outputArray[k]) {

flag = true;

}

}

if (flag == false) {

outputArray.push(array[j]);

}

flag = false;

}

// tArray = [100, 23, 67, 45]

老手

let array = [100, 23, 23, 23, 23, 67, 45];

let outputArray = Array.from(new Set(array))

6. 数组到对象

---

新手

let arr = [“value1”, “value2”, “value3”];

let arrObject = {};

for (let i = 0; i < arr.length; ++i) {

if (arr[i] !== undefined) {

arrObject[i] = arr[i];

}

}

老手

let arr = [“value1”, “value2”, “value3”];

let arrObject = {…arr};

7.对象到数组

---

新手

let number = {

one: 1,

two: 2,

};

let keys = [];

for (let numbers in numbers) {

if (number.hasOwnProperty(number)) {

keys.push(number);

}

}

// key = [ ‘one’, ‘two’ ]

老手

let number = {

one: 1,

two: 2,

};

let key = Object.keys(numbers); // key = [ ‘one’, ‘two’ ]

let value = Object.values(numbers); // value = [ 1, 2 ]

let entry = Object.entries(numbers); // entry = [[‘one’ : 1], [‘two’ : 2]]

8. 短路条件

---

新手

if (docs) {

goToDocs();

}

老手

docs && goToDocs()

9. 使用^检查数字是否相等

---

if(a!=123) // before // 一般开发者

if(a^123) // after // B格比较高的

10.对象遍历

---

const age = {

Rahul: 20,

max: 16

};

// 方案1：先得 key 在遍历key

const keys = Object.keys(age);

keys.forEach(key => age[key]++);

console.log(age); // { Rahul: 21, max: 16 }

// 方案2 - for...in 循环

for(let key in age){

age[key]++;

}

console.log(age); // { Rahul: 22, max: 18 }

11. 获取对象的所有键

---

cosnt obj = {

name: “前端小智”,

age: 16,

address: “厦门”,

profession: “前端开发”,

};

console.log(Object.keys(obj)); // name, age, address, profession

12.检查值是否为数组

---

const arr = [1, 2, 3];

console.log(typeof arr); // object

console.log(Array.isArray(arr)); // true

13.初始化大小为n的数组并填充默认值

---

const size = 5;

const defaultValue = 0;

const arr = Array(size).fill(defaultValue);

console.log(arr); // [0, 0, 0, 0, 0]

14. 真值和虚值

---

虚值：false,0, "",null,undefined和NaN。