JavaScript 箭头函数中的问题

Question

我是新手我已经在此链接中下载了一些源 https://github.com/the-road-to-learn-react/react-redux-example 我在文件 src/app.js 第 4 行中有一些问题const applyFilter = searchTerm => article =>  article.title.toLowerCase().includes(searchTerm.toLowerCase());为什么这不能与const applyFilter = searchTerm => article =>{  article.title.toLowerCase().includes(searchTerm.toLowerCase());} 或者const applyFilter = searchTerm => {article =>  article.title.toLowerCase().includes(searchTerm.toLowerCase());}并在第 14 行调用函数时articles.filter(applyFilter(searchTerm))const applyFilter = searchTerm => article =>  article.title.toLowerCase().includes(searchTerm.toLowerCase());这在我看来是在箭头函数内调用箭头函数？他们怎么能把 var 'article' 放进去？

Answer 1

箭头函数语法有点像这样

(a) => b(a);

is equivalent to

function(a) {

    return b(a);

}

但是，当您添加{}到箭头函数时，它会改变含义：

(a) => { b(a); }

is equivalent to

function(a) {

    b(a); 

    // notice that this doesn't actually return anything, 

    // it just calls a function and does nothing with the result

}

所以加括号的时候要加return语句

(a) => { return b(a); }