Question
The new [ES6 arrow functions](https://developer.mozilla.org/en-
US/docs/Web/JavaScript/Reference/Functions/Arrow_functions) say return is
implicit under some circumstances:
The expression is also the implicit return value of that function.
In what cases do I need to use return with ES6 arrow functions?
Answer
Jackson has partially answered this in a similar question:
Implicit return, but only if there is no block.
- 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 returnsundefined. Those braces are an explicit block.id:is a label.
I would add to this the definition of a [block](https://developer.mozilla.org/en- US/docs/Web/JavaScript/Reference/Statements/block):
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.
Examples :
// 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')
