Shulou(Shulou.com)06/03 Report--

JavaScript shorthand writing what, I believe that many inexperienced people are helpless about this, this article summarizes the causes of the problem and solutions, through this article I hope you can solve this problem.

1. ternary operator

When you want to write if... Use ternary operators instead of else statements.

Common spelling:

const x = 20;let answer;if (x > 10) { answer = 'is greater';} else { answer = 'is lesser';}

Abbreviations:

const answer = x > 10 ? 'is greater' : 'is lesser';

It is also possible to nest if statements:

const big = x > 10 ? " greater 10" : x

2. short circuit evaluation shorthand

When assigning another value to a variable, you want to make sure that the original value is not null, undefined, or empty. You can write an if statement with multiple conditions.

if (variable1 !== null || variable1 !== undefined || variable1 !== '') { let variable2 = variable1;}

Or you can use the short-circuit evaluation method:

const variable2 = variable1 || 'new';

3. Declaring variable shorthand methods

let x;let y;let z = 3;

Abbreviations:

let x, y, z=3;

4.If there is a conditional shorthand method

if (likeJavaScript === true)

Abbreviations:

if (likeJavaScript)

The two statements are equal only if likeJavaScript is true

If the judgment value is not true, it can be as follows:

let a;if ( a !== true ) {// do something...}

Abbreviations:

let a;if ( ! a ) {// do something...}

5. JavaScript loop shorthand

for (let i = 0; i

< allImgs.length; i++) 简写： for (let index in allImgs) 也可以使用Array.forEach： function logArrayElements(element, index, array) { console.log("a[" + index + "] = " + element);}[2, 5, 9].forEach(logArrayElements);// logs:// a[0] = 2// a[1] = 5// a[2] = 9 6.短路评价 给一个变量分配的值是通过判断其值是否为null或undefined，则可以： let dbHost;if (process.env.DB_HOST) { dbHost = process.env.DB_HOST;} else { dbHost = 'localhost';} 简写： const dbHost = process.env.DB_HOST || 'localhost'; 7.十进制指数 当需要写数字带有很多零时（如10000000），可以采用指数（1e7）来代替这个数字： for (let i = 0; i < 10000000; i++) {} 简写： for (let i = 0; i < 1e7; i++) {}// 下面都是返回true1e0 === 1;1e1 === 10;1e2 === 100;1e3 === 1000;1e4 === 10000;1e5 === 100000; 8.对象属性简写 如果属性名与key名相同，则可以采用ES6的方法： const obj = { x:x, y:y }; 简写： const obj = { x, y }; 9.箭头函数简写 传统函数编写方法很容易让人理解和编写，但是当嵌套在另一个函数中，则这些优势就荡然无存。 function sayHello(name) { console.log('Hello', name);}setTimeout(function() { console.log('Loaded')}, 2000);list.forEach(function(item) { console.log(item);}); 简写： sayHello = name =>

console.log('Hello', name);setTimeout(() => console.log('Loaded'), 2000);list.forEach(item => console.log(item));

10.隐式返回值简写

经常使用return语句来返回函数最终结果，一个单独语句的箭头函数能隐式返回其值（函数必须省略{}为了省略return关键字）

为返回多行语句（例如对象字面表达式），则需要使用()包围函数体。

function calcCircumference(diameter) { return Math.PI * diameter}var func = function func() { return { foo: 1 };};

简写：

calcCircumference = diameter => ( Math.PI * diameter;)var func = () => ({ foo: 1 });

11.默认参数值

为了给函数中参数传递默认值，通常使用if语句来编写，但是使用ES6定义默认值，则会很简洁：

function volume(l, w, h) { if (w === undefined) w = 3; if (h === undefined) h = 4; return l * w * h;}

简写：

volume = (l, w = 3, h = 4 ) => (l * w * h);volume(2) //output: 24

12.模板字符串

传统的JavaScript语言，输出模板通常是这样写的。

const welcome = 'You have logged in as ' + first + ' ' + last + '.'const db = 'http://' + host + ':' + port + '/' + database;

ES6可以使用反引号和${}简写：

const welcome = `You have logged in as ${first} ${last}`;const db = `http://${host}:${port}/${database}`;

13.解构赋值简写方法

在web框架中，经常需要从组件和API之间来回传递数组或对象字面形式的数据，然后需要解构它

const observable = require('mobx/observable');const action = require('mobx/action');const runInAction = require('mobx/runInAction');const store = this.props.store;const form = this.props.form;const loading = this.props.loading;const errors = this.props.errors;const entity = this.props.entity;

简写：

import { observable, action, runInAction } from 'mobx';const { store, form, loading, errors, entity } = this.props;

也可以分配变量名：

const { store, form, loading, errors, entity:contact } = this.props;//最后一个变量名为contact

14.多行字符串简写

需要输出多行字符串，需要使用+来拼接：

const lorem = 'Lorem ipsum dolor sit amet, consectetur\n\t' + 'adipisicing elit, sed do eiusmod tempor incididunt\n\t' + 'ut labore et dolore magna aliqua. Ut enim ad minim\n\t' + 'veniam, quis nostrud exercitation ullamco laboris\n\t' + 'nisi ut aliquip ex ea commodo consequat. Duis aute\n\t' + 'irure dolor in reprehenderit in voluptate velit esse.\n\t'

使用反引号，则可以达到简写作用：

const lorem = `Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse.`

15.扩展运算符简写

扩展运算符有几种用例让JavaScript代码更加有效使用，可以用来代替某个数组函数。

// joining arraysconst odd = [1, 3, 5];const nums = [2 ,4 , 6].concat(odd);// cloning arraysconst arr = [1, 2, 3, 4];const arr2 = arr.slice()

简写：

// joining arraysconst odd = [1, 3, 5 ];const nums = [2 ,4 , 6, ...odd];console.log(nums); // [ 2, 4, 6, 1, 3, 5 ]// cloning arraysconst arr = [1, 2, 3, 4];const arr2 = [...arr];

不像concat()函数，可以使用扩展运算符来在一个数组中任意处插入另一个数组。

const odd = [1, 3, 5 ];const nums = [2, ...odd, 4 , 6];

也可以使用扩展运算符解构：

const { a, b, ...z } = { a: 1, b: 2, c: 3, d: 4 };console.log(a) // 1console.log(b) // 2console.log(z) // { c: 3, d: 4 }

16.强制参数简写

JavaScript中如果没有向函数参数传递值，则参数为undefined。为了增强参数赋值，可以使用if语句来抛出异常，或使用强制参数简写方法。

function foo(bar) { if(bar === undefined) { throw new Error('Missing parameter!'); } return bar;}

简写：

mandatory = () => { throw new Error('Missing parameter!');}foo = (bar = mandatory()) => { return bar;}

17.Array.find简写

想从数组中查找某个值，则需要循环。在ES6中，find()函数能实现同样效果。

const pets = [ { type: 'Dog', name: 'Max'}, { type: 'Cat', name: 'Karl'}, { type: 'Dog', name: 'Tommy'},]function findDog(name) { for(let i = 0; i pet.type ==='Dog' && pet.name === 'Tommy');console.log(pet); // { type: 'Dog', name: 'Tommy' }

18.Object[key]简写

考虑一个验证函数

function validate(values) { if(!values.first) return false; if(!values.last) return false; return true;}console.log(validate({first:'Bruce',last:'Wayne'})); // true

假设当需要不同域和规则来验证，能否编写一个通用函数在运行时确认？

// 对象验证规则const schema = { first: { required:true }, last: { required:true }}// 通用验证函数const validate = (schema, values) => { for(field in schema) { if(schema[field].required) { if(!values[field]) { return false; } } } return true;}console.log(validate(schema, {first:'Bruce'})); // falseconsole.log(validate(schema, {first:'Bruce',last:'Wayne'})); // true

现在可以有适用于各种情况的验证函数，不需要为了每个而编写自定义验证函数了

19.双重非位运算简写

有一个有效用例用于双重非运算操作符。可以用来代替Math.floor()，其优势在于运行更快，可以阅读此文章了解更多位运算。

Math.floor(4.9) === 4 //true

简写

~~4.9 === 4 //true看完上述内容，你们掌握JavaScript的简写写法有哪些的方法了吗？如果还想学到更多技能或想了解更多相关内容，欢迎关注行业资讯频道，感谢各位的阅读!

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