本文來(lái)源于多年的 JavaScript 編碼技術(shù)經(jīng)驗(yàn),，適合所有正在使用 JavaScript 編程的開(kāi)發(fā)人員閱讀。

本文的目的在于幫助大家更加熟練的運(yùn)用 JavaScript 語(yǔ)言來(lái)進(jìn)行開(kāi)發(fā)工作,。

文章將分成初級(jí)篇和高級(jí)篇兩部分,，分別進(jìn)行介紹。

const x = 20;

let answer;

if (x > 10) {

    answer = 'greater than 10';

} else {

    answer = 'less than 10';

}

const answer = x > 10 ? 'greater than 10' : 'less than 10';

for (let i = 0; i < allImgs.length; i )

for (let index of allImgs)

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

let x;

let y;

let z = 3;

let x, y, z=3;

if (likeJavaScript === true)

if (likeJavaScript)

for (let i = 0; i < 10000; i ) { }

for (let i = 0; i < 1e7; i ) { }

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'

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.`

if (variable1 !== null || variable1 !== undefined || variable1 !== '') {

     let variable2 = variable1;

}

const variable2 = variable1  || 'new';

let variable1;

let variable2 = variable1  || '';

console.log(variable2 === ''); // prints true

variable1 = 'foo';

variable2 = variable1  || '';

console.log(variable2); // prints foo

let dbHost;

if (process.env.DB_HOST) {

  dbHost = process.env.DB_HOST;

} else {

  dbHost = 'localhost';

}

const dbHost = process.env.DB_HOST || 'localhost';

const obj = { x:x, y:y };

const obj = { x, y };

function sayHello(name) {

  console.log('Hello', name);

}

setTimeout(function() {

  console.log('Loaded')

}, 2000);

list.forEach(function(item) {

  console.log(item);

});

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

function calcCircumference(diameter) {

  return Math.PI * diameter

}

calcCircumference = diameter => (

  Math.PI * diameter;

)

function volume(l, w, h) {

  if (w === undefined)

    w = 3;

  if (h === undefined)

    h = 4;

  return l * w * h;

}

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

const welcome = 'You have logged in as ' first ' ' last '.'

const db = 'http://' host ':' port '/' database;

const welcome = `You have logged in as ${first} ${last}`;

const db = `http://${host}:${port}/${database}`;

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;

import { observable, action, runInAction } from 'mobx';

const { store, form, loading, errors, entity } = this.props;

const { store, form, loading, errors, entity:contact } = this.props;

// joining arrays

const odd = [1, 3, 5];

const nums = [2 ,4 , 6].concat(odd);

// cloning arrays

const arr = [1, 2, 3, 4];

const arr2 = arr.slice( )

// joining arrays

const odd = [1, 3, 5 ];

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

console.log(nums); // [ 2, 4, 6, 1, 3, 5 ]

// cloning arrays

const arr = [1, 2, 3, 4];

const arr2 = [...arr];

const odd = [1, 3, 5 ];

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

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

console.log(b) // 2

console.log(z) // { c: 3, d: 4 }

function foo(bar) {

  if(bar === undefined) {

    throw new Error('Missing parameter!');

  }

  return bar;

}

mandatory = ( ) => {

  throw new Error('Missing parameter!');

}

foo = (bar = mandatory( )) => {

  return bar;

}

const pets = [

  { type: 'Dog', name: 'Max'},

  { type: 'Cat', name: 'Karl'},

  { type: 'Dog', name: 'Tommy'},

]

function findDog(name) {

  for(let i = 0; i<pets.length; i) {

    if(pets[i].type === 'Dog' && pets[i].name === name) {

      return pets[i];

    }

  }

}

pet = pets.find(pet => pet.type ==='Dog' && pet.name === 'Tommy');
console.log(pet); // { type: 'Dog', name: 'Tommy' }

function validate(values) {

  if(!values.first)

    return false;

  if(!values.last)

    return false;

  return true;

}

console.log(validate({first:'Bruce',last:'Wayne'})); // true

// object validation rules

const schema = {

  first: {

    required:true

  },

  last: {

    required:true

  }

}

// universal validation function

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'})); // false

console.log(validate(schema, {first:'Bruce',last:'Wayne'})); // true

Math.floor(4.9) === 4  //true

~~4.9 === 4  //true