我在一本书“Angular，第二版入门”中偶然发现了箭头函数的代码。 
 
let isPrime: (n: number) => boolean = n => { 
// body 
};
 
 我想确认这个故障的正确性。 
 
 
 
 let isPrime =函数名称“isPrime” 
 
 
 (n: number) =输入参数编号“n” 
 
 
 => boolean =箭头函数来检查布尔值（放置逻辑的地方） 
 
 
 =n =我没有得到这部分。 这是否意味着如果我把“逻辑在第三步找到素数”和真，你会得到满足我的逻辑的“n”？ 
 
 
 => {} =我可以在这里放置返回或其他逻辑来进行最终处理。 
 
 
 最后一个问题是有多少箭头函数对链接或曲线来说太多了？ 
 
 我相信@Fenton为我的理解给予了明确的解释。 
 
 @Sebastien给我的答案让我意识到我对箭头函数的错误解释; 等号和箭头符号并不总是指向函数，并且也可以表示数据类型。 
 
 下面是我接受的答案的组合版本。 
 
 类型 
 
 现在我们来描述这个函数的类型，它是一个数字，并返回一个布尔值。 
 
//correct usage : return boolean
let isPrime: (n: number) => boolean = n => { 
    // body
    return true
};

//incorrect usage
let isPrime: (n: number) => boolean = n => { 
    // body
    return "wrong"
};
 
 简单 
 
 我想我会写下如下，除非我有充分的理由使用箭头功能！ 
 
//correct usage : return boolean
function isPrime(n: number): boolean {
    // body
    return true;
}
//incorrect usage
function isPrime(n: number): boolean {
    // body
    return "wrong";
}
 
 我最后的测试就是这样。 
 
let isRightLogic: (n: number) => { host: boolean } = n => { 
   return { host: true };
}
console.log(isRightLogic(1)); // always return true but you get the idea.

I stumble upon below code of arrow function in a book "Getting Started with Angular, Second Edition". 
 
let isPrime: (n: number) => boolean = n => { 
// body 
};
 
I want to confirm correctness of this breakdown.
 
 
 
let isPrime = function name "isPrime"
 
 
(n: number) = input parameter number "n"
 
 
=> boolean = arrow function to check boolean (a place to put the logic)
 
 
=n = i don't get this part. does this mean if i put "logic to find prime number in third step" and true, you get "n" that satisfy my logic? 
 
 
=> {} = i can put return or other logic here for final process. 
 
 
The last question is how many arrow functions is too much for chaining or curring? 
 
I believe @Fenton give clear explanation for my understanding.
 
@Sebastien gives me answer that make me realise my wrong interpretation to arrow function ; equal and arrow sign doesn't always point to function, and can represent datatype too. 
 
below is combined version of my accepted answer.
 
Types
 
Now let's describe the types for this function, which are that is takes in a number, and gives back a boolean.
 
//correct usage : return boolean
let isPrime: (n: number) => boolean = n => { 
    // body
    return true
};

//incorrect usage
let isPrime: (n: number) => boolean = n => { 
    // body
    return "wrong"
};
 
Simple
 
I suppose that I would write it as below, unless I had a good reason to use an arrow function!
 
//correct usage : return boolean
function isPrime(n: number): boolean {
    // body
    return true;
}
//incorrect usage
function isPrime(n: number): boolean {
    // body
    return "wrong";
}
 
My final test is like this.
 
let isRightLogic: (n: number) => { host: boolean } = n => { 
   return { host: true };
}
console.log(isRightLogic(1)); // always return true but you get the idea.

原文：https://stackoverflow.com/questions/48447364