杰克逊在一个类似的问题中部分回答了这个问题：

隐式返回，但前提是没有阻塞。

• 当单行扩展为多行并且程序员忘记添加return.
• 隐式返回在语法上是模棱两可的。(name) => {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。
  

我会添加一个块的定义：

块语句（或其他语言中的复合语句）用于对零个或多个语句进行分组。该块由一对大括号分隔。

例子 ：

// 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')