Conditionally set an object property

Is there some syntax for setting properties based on a condition?

data: {
    userId: 7,
    actionId: 36,
    express: (myCondition ? true : null) // does not work
}

I want express to be either set to a value or not set at all (i.e., there should be no key named express), and without extra statements after the definition. I know I can use it as a boolean, but the receiving side is using an isset() check and I'm wondering if I can avoid modifying it.

---

Edit: Seems there is no direct solution to the problem as stated. Here are the close suggestions:

JSON.stringify (Chris Kessel, dystroy):

var json = JSON.stringify( {
    data: {
        userId: 7,
        actionId: 36,
        express: (myCondition ? true : null)
    }
});

An anonymous function (Paulpro):

var data = new function(){
    this.userId = 7;
    this.actionId = 36;
    myCondition && (this.express = true);
};

An extra statement (x4rf41):

data: {
    userId: 7,
    actionId: 36
}
if(myCondition) data["express"] = true;

Eval (a former colleague of mine):

eval("data = {userId: 7, actionId: 36 " + (myCondition ? ", express: true}" : "}"))

Conditional definition (don't really know how to label this one):

data = (
    (myCondition && { userId: 7, actionId: 36, express: true }) ||
    (!myCondition && { userId: 7, actionId: 36 })
);

Use the spread operator.

data: {
    userId: 7,
    actionId: 36,
    ...myCondition && {express: true}
}

Note that if you're using Flow, that syntax might generate type check errors. You can write the above more explicitly, and less succinctly, as:

data: {
    userId: 7,
    actionId: 36,
    ...(myCondition ? {express: true} : {})
}

Do it like this :

data: {
    userId: 7,
    actionId: 36,
    express: (myCondition ? true : undefined)
}

A property whose value is undefined isn't written when you stringify the object to JSON.

---

EDIT : It appears from the comments that there is no JSON involved in fact. OP is using $.ajax so $.param is probably used. $.param, unfortunately, does create an entry for properties whose value is undefined. So there's probably no solution without any supplementary line of code.

You can do it if you define your object using an anonymous function instead of object literal notation:

var data = new function(){
    this.userId = 7;
    this.actionId = 36;
    myCondition && (this.express = true);
};

The resulting data object is the exact same, except it's constructor will be the anonymous function instead of window.Object.

You could do something like this:

var json = JSON.stringify( {
    data: {
        userId: 7,
        actionId: 36,
        express: (myCondition ? true : null)
    }
});

A bit old but there is a good solution as well you can do :

data: {
    userId: 7,
    actionId: 36
}

Object.assign(data, !myCondition && { express: yourValue });

Thus it will assign your express property with the value you need if your condition is false.

The spread operator now fixes this. Here is an example with two comparisons.

Note: I changed date: to const date = so that it is valid runnable javascript. This can also be used with data: if it is supposed to be inside of a deep object structure.

const compareValue = 13;
const data =  {
    userId: 7,
    actionId: 36,
    ...(compareValue > 10 && {propertyForGreaterThan10: 'foo'}),
    ...(compareValue < 10 && {propertyForLessThan10: 'bar'}),
}
console.log(data);

first of all, thats javascript, not JSON.

the solution:

data: {
    userId: 7,
    actionId: 36
}
if(myCondition) data["express"] = true;