I want to include a property on an object only in the event that a variable is defined. I don't want the property at all otherwise. I don't even want it to equal a blank string. I'm thinking something like this:

someFunc({
    bing: "bing",
    bang: (myVar) ? myVar : undefined,
    boom: "boom"
    }, "yay");

In the event that myVar is undefined, I want this to result in the same thing as the below:

someFunc({
    bing: "bing",
    boom: "boom"
    }, "yay");

Am I doing it right?

I want to include a property on an object only in the event that a variable is defined. I don't want the property at all otherwise. I don't even want it to equal a blank string. I'm thinking something like this:

someFunc({
    bing: "bing",
    bang: (myVar) ? myVar : undefined,
    boom: "boom"
    }, "yay");

In the event that myVar is undefined, I want this to result in the same thing as the below:

someFunc({
    bing: "bing",
    boom: "boom"
    }, "yay");

Am I doing it right?

• javascript
• jquery

• 1 Looking back at it, I should probably have written (myVar === undefined) to prevent it matching a set false val. Anything else? – Matrym Commented Jan 28, 2011 at 20:08
• it all depends on which falsy values you want to leave out. undefined? null? 0? – Matt Ball Commented Jan 28, 2011 at 20:13
• The title requests a ternary expression, but the accepted answer does not contain a ternary expression. Boo! – LinuxDisciple Commented Jun 7, 2016 at 22:43

5 Answers 5

There is a difference between this:

var ex1 = {foo: undefined};

and this:

var ex2 = {};

Therefore, here's how I would do it:

var args = {
    bing: 'bing',
    boom: 'boom'
};

if (typeof myVar !== 'undefined') {
    args.bang = myVar;
}

someFunc(args, 'yay');

i would do something like

var config = {
    bing: "bing",
    boom: "boom"
};

if (typeof myVar !== 'undefined') config.bang = myVar;

someFunc(config, 'yay');

you have to be careful of javascript truthiness and falsiness. The if statement in my example only puts bang on config if myVar is defined, but it works if myVar is defined as false.

Use rest operator.

var obj = {
    bing: "bing",
    ...(myVar ? { bang: myVar } : {}),
    boom: "boom"
}

var obj = {
    bing: "bing",
    boom: "boom"
}

myVar != null && obj.bang = myVar;

someFunc(obj, "yay");

The above code gets the job done. I don't think that you can do it directly inside the function call.

The best way to do this would be

var args = {
    bing: "bing",
    bang: myVar,
    boom: "boom"
}

if (myVar === undefined) {
    delete args.myVar;
}

someFunc(args, "yay");

Clearly adding it when it exists is better then then deleting it when it doesn't exist.

The point is to treat something like it really isn't there it is safest to use the native delete to remove a property from an object.

You can hack it using setTimeout and callbacks. I remend againts this

var args = {
    bing: 4,
    bang: (myVar === undefined) ? (function() {
        setTimeout(function() {
            delete args.bang;
        }, 0);
    })() : myVar
}, "yay");