Javascript function always returns null

Question

I am newbie to the JavaScript world. I have a doubt how the return statement works in JavaScript.

What I am trying to do is to have a function pass one arguments param and looking whether the param match the key of the exampleData object. If match found I want to return the value and break the looping of each function also break the function I don't want to execute any other statement under the each function. If no match found the function must return null. But currently the function always return null value.

function exampleFunction(param){
    $.each(exampleData, function (key, value) {
        if(key == param){
        return value;
        }
    });
    return null;
}

Any insight into this would highly be appreciated. Thank you.

Are you sure that key and param match? Also, are you sure that value isn't null? — Douglas Barbin, Jul 31 '13 at 17:11
Your `return value;` is in a different function. Just use a `for-in` loop instead. — , Jul 31 '13 at 17:12
You don't need to do all this. `exampleData[param]` does almost the same thing. It is equal to `undefined` when param is not in exampleData — Paul, Jul 31 '13 at 17:13
possible duplicate of [Jquery each - Stop loop and return object](http://stackoverflow.com/questions/8224375/jquery-each-stop-loop-and-return-object) — apsillers, Jul 31 '13 at 17:14
@Paul is right. There's no need to loop at all, unless you actually need to the type coercion of the `==` operator. — , Jul 31 '13 at 17:14
possible duplicate of [Javascript function fails to return element](http://stackoverflow.com/questions/11569516/javascript-function-fails-to-return-element) — Bergi, Jul 31 '13 at 17:19

score 8 · Accepted Answer · answered Jul 31 '13 at 17:17

Your example doesn't seem to need a loop. That and returning from the loop-delegate doesn't do anything for you.

You can test if a key appears in an object using the in operator.

function exampleFunction(param){
  return param in exampleData ? exampleData[param] : null;
}

score 4 · Answer 2 · answered Jul 31 '13 at 17:13

4

Given Crazy Train's comment, you need to capture the matching value so you can return it later:

function exampleFunction(param) {
    var match = null;
    $.each(exampleData, function (key, value) {
        if (key == param) {
            match = value;
            return false; // to end the $.each early
        }
    });
    return match;
}

answered Jul 31 '13 at 17:13

Cᴏʀʏ

105,112
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Extra +1 for ending the each – mplungjan Jul 31 '13 at 17:15
There is no need to loop through exampleData. – Douglas Barbin Jul 31 '13 at 17:16
Unless you want to modify the value before returning it – mplungjan Jul 31 '13 at 17:17
Modifying the value makes no difference. – Jul 31 '13 at 17:18
I just offered the easiest correction to the OP's train of thought; I definitely agree that there are better solutions posted. – Cᴏʀʏ Jul 31 '13 at 18:17

Douglas Barbin · Answer 3 · 2013-07-31T17:20:42.387

0

Try this:

function exampleFunction(param){ 
    return exampleData[param];
  }

EDIT: If you want to return null if the parameter is undefined, then take a look at Paul and Crazy Train's comments:

return (typeof exampleData[param] === 'undefined')? null: exampleData[param];

OR

return (param in exampleData) ? exampleData[param] : null;

edited Jul 31 '13 at 17:20

answered Jul 31 '13 at 17:15

Douglas Barbin

3,595
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1

If it is null, it returns null. If it is undefined, it returns undefined. – Douglas Barbin Jul 31 '13 at 17:17
So if he wants null, the you need to test if it exists – mplungjan Jul 31 '13 at 17:18
`return (typeof exampleData[param] === 'undefined')? null: exampleData[param];` – Paul Jul 31 '13 at 17:19
Correct. So he would add that condition before the return, and return null if it doesn't exist. Assuming that's what he wants to do. – Douglas Barbin Jul 31 '13 at 17:19
`return (param in exampleData) ? exampleData[param] : null;` – Jul 31 '13 at 17:19
1

No need to copy everybody else's answers into yours – mplungjan Jul 31 '13 at 17:21
1

@mplungjan They are good suggestions, so I edited my answer to reflect that. No harm in expanding on an answer. – Douglas Barbin Jul 31 '13 at 17:22
I guess since `null == undefined` that's quite irrelevant – Bergi Jul 31 '13 at 17:23
2

Unless the caller is testing `=== null`. – Jul 31 '13 at 17:23
Testing for `typeof x[key] === "undefined"` can have unexpected results. It may be that the key is present but its _value_ has been set to `undefined`. – canon Jul 31 '13 at 17:37

score 0 · Answer 4 · answered Jul 31 '13 at 17:17

There are a few issues with your approach:

The inner function you defined is returning to $.each, not to the outer function, so you never get that value.
You don't need to iterate over the object in the wild way you are. Objects in Javascript are hash tables, you can simply do the following

:

function exampleFunction(param) {
    return exampleData[param];
}

If exampleData[param] is undefined, it will return undefined, otherwise, it will return the value stored there.

If you absolutely need the undefined case to return null instead of undefined, then it becomes a bit more complicated.

function exampleFunction(param) {
    if(exampleData.hasOwnProperty(param) {
        return exampleData[param];
    } else {
        return null;
    }
}

Javascript function always returns null

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