CODEWITHSUNDEEP
javascriptarrays
Lucas Ferronato
Lucas Ferronato

Reputation: 119

Array map returning array of undefined when should return array of objects

Why does

['a', 'b', 'c'].map((x) => { letter: x }) returns a array of undefined

and

['a', 'b', 'c'].map((x) => [{ letter: x }][0]) returns a array of objects correctly?

Upvotes: 3

Views: 1962

Answers (3)

hsj
hsj

Reputation: 68

A function that lacks an explicit return statement will return undefined. () => {} is equivalent to function(){}. x => x is equivalent to function(x){ return x;}

So arrow function without {} will return computed value of the expression.

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386848

Because

  • You use the curly brackets as block statement.

  • You have letter as a label.

  • x is just a value without some action.

  • The return of undefined is the standard return value of a function without any return statement with value.

    To return a value other than the default, a function must have a return statement that specifies the value to return. A function without a return statement will return a default value. In the case of a constructor called with the new keyword, the default value is the value of its this parameter. For all other functions, the default return value is undefined.

Correct call for mapping objects.

console.log(['a', 'b', 'c'].map(x => ({ letter: x })));

Upvotes: 2

Nenad Vracar
Nenad Vracar

Reputation: 122115

You need to wrap object in ()

var result = ['a', 'b', 'c'].map((x) => ({ letter: x }))
console.log(result)

Upvotes: 2

Related Questions