javascript function returns undefined instead of object literal

Question

I just started working a bit with javascript but quickly got stuck with a - in my eyes - quite simple task of returning an object literal.

The code I currently have looks like this

function wrapInObject(x)
{
    return
    {
        y: x
    };
}
console.log(wrapInObject('someValue'));

but instead of writing the object literal to the console it prints undefined - I tried calling the function with numbers or other object literals but nothing helped.

Thanks for any help!

Yep, white space is killing you. remove the return after the return — epascarello, Jul 27 '16 at 18:34
Wow - thx a lot guys! No commercial expensive support etc. could be faster :D — tengobash, Jul 27 '16 at 18:37
That is the reason why you should always write your functions like `function f() {...` or object literal expressions like `return {...`. — , Jul 27 '16 at 18:38

DAXaholic · Accepted Answer · 2016-07-27T18:39:03.407

3

This is due to a process known as automatic semicolon insertion and is quite often the source of confusion for new devs with a C# background or other languages where placing the opening brace on a new line is common practice.

Essentially what happens is that an implicit semicolon is placed right after your return statement so that it returns undefined and your object literal is never 'reached'.

To fix it just move the opening brace to the end of the return like so

function wrapInObject(x)
{
    return { 
        y: x 
    };
}

edited Jul 27 '16 at 18:39

answered Jul 27 '16 at 18:34

DAXaholic

28,212
5
58
67

1

Good catch. I copy pasted the code and it worked because my text editor fixed the carriage return. – Isabel Inc Jul 27 '16 at 18:36

score 0 · Answer 2 · answered Jul 27 '16 at 18:35

Because of automatic semicolon insertion

function wrapInObject(x)
{
    return
    {
        y: x
    };
}
console.log(wrapInObject('someValue'));

gets converted to

function wrapInObject(x)
{
    return ; // semicolon is added
    {
        y: x
    };
}
console.log(wrapInObject('someValue'));

Hence you get undefined.

score 0 · Answer 3 · edited May 23 '17 at 12:14

0

This is because of semicolon auto-insertion adding a line break after the return statement makes the js engine parse that line as if there was a semicolon. Move the opening bracket to the same line as the return statement.

Another StackOverflow entry about semicolon auto-insertion

edited May 23 '17 at 12:14

Community

1
1

answered Jul 27 '16 at 18:35

Nicholas

2,538
1
17
18

javascript function returns undefined instead of object literal

3 Answers3