三元操作符
var x = 20 , answer;
if (x > 10) {
answer = 'is greater';
} else {
answer = 'is lesser';
}
//简写
var answer = x > 10 ? 'is greater' : 'is lesser';
//
var answer = x > 10 ? 'is greater' : x;
短路求值
当给一个变量分配另一个值时，想确定源始值不是null或undefined或空值 0。
if (variable1 !== null || variable1 !== undefined || variable1 !== ''||variable1 !== 0) {
var variable2 = variable1;
}
//简写
var variable2 = variable1 || 'new';
声明变量
var x;
var y;
var z=3;
//简写
var x,y,z=3;
if存在条件
if (a === true)
//
if (a)
if ( a !== true )
//
if ( !a )
JavaScript循环
for (var i = 0; i < arr.length; i++)
for (var i in arr)
也可以Array.forEach
function logArrayElements(element, index, array) {
console.log("a[" + index + "] = " + element);
}
[2, 5, 9].forEach(logArrayElements);
// a[0] = 2
// a[1] = 5
// a[2] = 9
十进制指数
for (let i = 0; i < 10000; i++)
//
for (let i = 0; i < 1e7; i++)
1e0 === 1;
1e1 === 10;
1e2 === 100;
1e3 === 1000;
1e4 === 10000;
1e5 === 100000;
对象属性
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 };
箭头函数
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) );
隐式返回值
es6
function calcCircumference(diameter) {
return Math.PI * diameter
}
var func = function func() {
return { foo: 1 };
};
calcCircumference = diameter => (
Math.PI * diameter;
)
var func = () => ({ foo: 1 });
默认参数值
es6
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);
模板字符串
es6
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}`;
解构赋值
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;
分配变量名
const { store, form, loading, errors, entity:contact } = this.props;
多行字符串
es6
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'
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
扩展运算符
es6
// 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];
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];
强制参数
function foo(bar) {
if(bar === undefined) {
throw new Error('Missing parameter!');
}
return bar;
}
mandatory = () => {
throw new Error('Missing parameter!');
}
foo = (bar = mandatory()) => {
return bar;
}
Array.find
es6
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 === Tommy) {
return pets[i];
}
}
}
pet = pets.find(pet => pet.type ==='Dog' && pet.name === 'Tommy');
