ECMAScript 6 中的快捷语法汇总及代码示例

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

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

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

const variable2 = variable1  || ‘new‘;

let x;
let y;
let z = 3;

let x, y, z=3;

if (likeJavaScript === true)

if (likeJavaScript)

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

for (let index in 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

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

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

// All the below will evaluate to true
1e0 === 1;
1e1 === 10;
1e2 === 100;
1e3 === 1000;
1e4 === 10000;
1e5 === 100000;

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;

// 或者

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

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.`

// 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];

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