安装nodejs
略
安装vscode
略
1.单行箭头表达式:
//隐含省略了return let foo = (arg1,arg2) => arg1 + arg2; //上述表达式相当于 // let foo = function (arg1, arg2) { return arg1 + arg2; }; let result = foo(1,3) console.log(result)
2.多行箭头表达式(函数代码有多行，必须使用{}大括号，必须写return):
let foo = (arg1, agr2) => { let result = arg1 + agr2 return result; } let result = foo(1,3) console.log(result)
3.无参数:
let foo = () => {} //以上表达式相当于 let foo = function () {}
4.一个参数(无需使用()小括号):
let foo = arg => { return arg*arg; } let result = foo(3) console.log(result)
5 例子
let arr = [1,2,3,4,5]; console.log(arr.filter(value => value%2 == 0)) //以上代码相当于 let arr = [1, 2, 3, 4, 5]; console.log(arr.filter(function (value) { return value % 2 == 0; })); //[2,4]返回被2整除的值
6.箭头表达式中的this关键字:
箭头函数不会创建自己的this,它只会从自己的作用域链的上一层继承this
(1)ES5方式(计时器中无法找到this)
function Foo (name) { this.name = name; setInterval(function () { console.log(this.name); },1000); } let foo = new Foo('莎士比亚'); //返回name is---无法找到this.name
(2)ES6方式(计时器中可以找到this)
function Foo (name) { this.name = name; setInterval(() => { console.log(this.name); },1000); } let foo = new Foo("莎士比亚"); //莎士比亚
箭头函数的嵌套
关于箭头函数嵌套，也称为函数柯里化
function add(a, b) { return a + b; }
function add(a) { return function(b) { return a + b; } } console.log(add(4)(5)); //输出9
箭头函数柯里化
const add = (a) => (b) => a + b; console.log(add(4)(5)); //输出9
react中的使用
类似react-redux的connect代码
const VisibleTodoList = connect( mapStateToProps, mapDispatchToProps )(TodoList)
