TypeScript箭头函数（第2篇）

Posted 2021-02-28 music-liang

let listA:number[] = [1,2,3];
listA.push(4);
let listB:Array<number>=[1,2,3];
console.dir(listA);
console.dir(listB);

let mySum = function(x:number, y:number):number{
    return x+y;
}
console.log(mySum(1,2));

let mySum2 = (x:number, y:number):number=>x+y;
console.log(mySum2(2,3));


///对右侧匿名函数进行类型定义  (x:number, y:number)=>number 
let mySum3:(x:number, y:number)=>number = function(x:number, y:number):number{
    return x+y;
}
console.log(mySum3(3,4));

///如果只有一条语句，不仅省掉了"{}"，连 "return" 都给省掉了.  mySum4和mySum5等价
let mySum4:(x:number, y:number)=>number = (x:number, y:number):number => x+y;
let mySum5:(x:number, y:number)=>number = (x:number, y:number):number => { return x+y};
console.log(mySum4(5,6));
console.log(mySum5(5,6));

let mySum6:(x:number, y:number)=>void = (x:number, y:number):void => {  
    x = x+y; 
    console.log(x);
};
mySum6(100,200);


///箭头函数返回一个对象
let getTempData = (id:number) =>({
    userID:id,
    name:"Henry"
});

console.log(getTempData(666));
console.log(getTempData(666).userID);
console.log(getTempData(666).name);


///不带参数，有返回值
let mySum7 = ():number=>{
    ///do something...
    return 666;
};

//不带参数，没有返回值
let mySum8 = ()=>{
    ///do something...
    return 666;
};

function doesNotReturn()
{
    console.log("---doesNotReturn---");
}

//不带参数，没有返回值，而且只有一条语句
let mySum9 = () => void doesNotReturn();
///执行 右侧的函数.没有返回值..
mySum9();


const isEven = (n:number) => n % 2 === 0 ;
const square = (n:number) => n * n;
console.log(isEven(1));
console.log(isEven(2));


// 箭头函数写法
let test1 = [1,2,3];
console.dir(test1.map(x => x * x));
console.dir(test1);



// 正常函数写法
let values1 = [6,4,2,1,5,3];
let values2 = [5,3,2,1,4,6];
var result1 = values1.sort(function (a, b) {
    return a - b;
  });
  
// 箭头函数写法
var result2 = values2.sort((a, b) => a - b);
console.log(result1);
console.log(result2);



//=============嵌套的箭头函数
let insert = (value:number) => (
    {into: (array:Array<number>) => (
        {after: (afterValue:number) => {
            array.splice(array.indexOf(afterValue) + 1, 0, value);
            return array;
        }
    }
    )
}
);  
//把某个数，插入到数组中某个元素后面
console.log(insert(5).into([4, 5, 6, 7]).after(6)); 

 

参考地址：

https://es6.ruanyifeng.com/#docs/function#%E7%AE%AD%E5%A4%B4%E5%87%BD%E6%95%B0

 https://www.jianshu.com/p/f97fc6bc0d56