Dynamically add to object and create if undefined?

Question

I'm having a hard time searching/explaining what I'm trying to do, but I want to add data to a JavaScript object. The index that I want to add the data to may or may not exist, and that index name will be dynamic, so I can't just define all the objects at the start.

Lets say I'm adding to an object when users click links on my site. I've defined my object:

exampleObject = {};

If a user clicks a fruit link, I want to add the fruit to the object. I would normally do this:

exampleObject.fruit = {};
exampleObject.fruit.strawberry = true;

My issue is that I don't want to overwrite the object when the user clicks the next fruit. I would need to check if the object is defined and then add to it:

if ( typeof exampleObject.fruit === 'undefined' ){
    exampleObject.fruit = {};
    exampleObject.fruit.cherry = true;
} else {
    exampleObject.fruit.cherry = true;
}

What I'm wondering is if there is a shorthand way of doing the conditional above? I was hoping for a one-liner since I'll be doing this a lot. My next thought was to make a function for this, but I don't want to have to reinvent the wheel or restrict myself (like, if I want to use an array within this object to push all fruits into one index). jQuery is an option in this case, but not necessarily my first choice.

Thiago Custodio · Accepted Answer · 2015-12-15 16:14:21Z

2

exampleObject = exampleObject || {};
exampleObject.fruit = exampleObject.fruit || {};
exampleObject.fruit.cherry = true;

answered Dec 15, 2015 at 16:14

Thiago Custodio

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Comments

shennan · Accepted Answer · 2015-12-15 16:23:36Z

1

Based on the fact that you have said the index name will be dynamic, use square brackets to adjust the object key/index:

function addFruit (name) {

  exampleObject = exampleObject || {};
  exampleObject.fruit = exampleObject.fruit || {};

  if (typeof exampleObject.fruit[name] == 'undefined')
    exampleObject.fruit[name] = true;

}

edited Dec 15, 2015 at 16:23

answered Dec 15, 2015 at 16:17

shennan

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1 Comment

GreatBlakes Over a year ago

This is along the lines of what I was thinking about doing with the function- appreciate the answer. I got it working using your response as my starting point (with a dynamic index like Brad suggested). Thanks.

Brad · Accepted Answer · 2015-12-15 16:36:40Z

1

I would go the function route, depending on how extreme your new indexes are. This will allow you to assign category and item in one go.

function checkOrAddKey(key, newItem) {
  if(!exampleObject.hasOwnProperty(key)) {
    exampleObject[key] = {};
    exampleObject[key][newItem] = true;
  }
  else {
    exampleObject[key][newItem] = true;
  }
}

checkOrAddKey('fruit', 'apple');
checkOrAddKey('fruit', 'banana');
checkOrAddKey('scone', 'cinnamon');

//exampleObject: { fruit: { apple: true, banana: true }, scone: { cinnamon: true } }

answered Dec 15, 2015 at 16:36

Brad

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