什么时候应该在 ES6 箭头函数中使用 return 语句 [英] When should I use a return statement in ES6 arrow functions

问题描述

新的 ES6 箭头函数说return 在某些情况下是隐式的:

The new ES6 arrow functions say return is implicit under some circumstances:

该表达式也是该函数的隐式返回值.

The expression is also the implicit return value of that function.

在什么情况下我需要将 return 与 ES6 箭头函数一起使用?

In what cases do I need to use return with ES6 arrow functions?

推荐答案

Jackson 在类似问题中部分回答了这个:

Jackson has partially answered this in a similar question:

隐式返回，但前提是没有阻塞.

Implicit return, but only if there is no block.

• 当一行扩展为多行并且程序员忘记添加return时，这将导致错误.
• 隐式返回在语法上不明确.<代码>(名称)=>{id: name} 返回对象 {id: name}... 对吗?错误的.它返回 undefined.这些大括号是一个显式块.id: 是一个标签.

• This will result in errors when a one-liner expands to multiple lines and the programmer forgets to add a return.
• Implicit return is syntactically ambiguous. (name) => {id: name}returns the object {id: name}... right? Wrong. It returns undefined. Those braces are an explicit block. id: is a label.

我会添加一个块的定义:

块语句(或其他语言的复合语句)用于组合零个或多个语句.该块由一对大括号分隔.

A block statement (or compound statement in other languages) is used to group zero or more statements. The block is delimited by a pair of curly brackets.

示例:

// returns: undefined
// explanation: an empty block with an implicit return
((name) => {})() 

// returns: 'Hi Jess'
// explanation: no block means implicit return
((name) => 'Hi ' + name)('Jess')

// returns: undefined
// explanation: explicit return required inside block, but is missing.
((name) => {'Hi ' + name})('Jess')

// returns: 'Hi Jess'
// explanation: explicit return in block exists
((name) => {return 'Hi ' + name})('Jess') 

// returns: undefined
// explanation: a block containing a single label. No explicit return.
// more: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label
((name) => {id: name})('Jess') 

// returns: {id: 'Jess'}
// explanation: implicit return of expression ( ) which evaluates to an object
((name) => ({id: name}))('Jess') 

// returns: {id: 'Jess'}
// explanation: explicit return inside block returns object
((name) => {return {id: name}})('Jess') 

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