javascript ignore-if-null operator?

Question

In javascript I have a lot of code like this.

if (ctrl && ctrl.main && ctrl.main.user) {
    SetTheme(ctrl.main.user.theme);
}

which is annoyingly long. In other, languages you can do simply

SetTheme(ctrl?.main?.user?.theme);

Is there any way to do that in javascript?

I tried,

function safeGet(a,b) { return a ? a[b] : null; }

and

SetTheme(safeGet(safeGet(safeGet(ctrl, 'main'), 'user'), 'theme'));

But that's not very readable.

The logical AND operator `&&` is your best bet in JavaScript. Anyway, this seems more like a rant about JS to me than a question. — TimoStaudinger, Dec 07 '16 at 16:26
*"Is there any way to do that in javascript?"* No. [There have been discussions about this](https://esdiscuss.org/topic/existential-operator-null-propagation-operator), but they haven't led anywhere yet. — Felix Kling, Dec 07 '16 at 16:33

Nina Scholz · Accepted Answer · 2016-12-07T16:47:37.757

2

The correct short cut could be

if (((ctrl || {}).main || {}).user) { // ...

Or you could use an array as path, or a dot separated string as path and check aginst existence and return the value.

function getValue(object, path) {
    return path.split('.').reduce(function (o, k) {
        return (o || {})[k];
    }, object);
}

var ctrl = { main: { user: { theme: 42 } } };

console.log(getValue(ctrl, "main.user.theme"));

edited Dec 07 '16 at 16:47

answered Dec 07 '16 at 16:32

Nina Scholz

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1

very nice. i like the use of the `||`. – John Henckel Dec 07 '16 at 18:55

score 1 · Answer 2 · answered Dec 07 '16 at 16:29

You could create a generic function to do this by passing it the string representing the path to the nested property you want:

  function getValue(object, prop, /*optional*/ valIfUndefined) {
            var propsArray = prop.split(".");
            while(propsArray.length > 0) {
                var currentProp = propsArray.shift();
                if (object.hasOwnProperty(currentProp)) {
                    object = object[currentProp];
                } else {
                    if (valIfUndefined) {
                        return valIfUndefined;
                    } else {
                        return undefined;
                    }
                }
            }

            return object;
        }

Then use this on any object like:

// This will return null if any object in the path doesn't exist
if (getValue(ctrl, 'main.user', null)) {
    // do something
}

I would assume that the lack of readability is in reference to the nested "saveGet" calls. This solution doesn't suffer from that issue. — mcgraphix, Dec 07 '16 at 16:32

javascript ignore-if-null operator?

2 Answers2