In Javascript, How to determine if an object property exists and is not empty?

Question

Suppose I have the next javascript object:

var errors = {
    error_1: "Error 1 description",
    error_2: "Error 2 description",
    error_3: "",
    error_4: "Error 4 description"
};

How can I determine if the property error_1 exists in the errors object and is not empty as well?

@Arvind In my case, they will be only strings. But if you ask to provide some solution for other data types, then that will be great, as me and the others will be able to use what fits for them. — Amr
– Amr, Commented Feb 17, 2015 at 0:51
What does "not empty" mean? Object properties are initialised to the supplied value, their default or undefined when created, so are never "empty". — RobG
– RobG, Commented Feb 17, 2015 at 1:02

AhmadAssaf · Accepted Answer · 2015-02-17 00:32:27Z

33

if (errors.hasOwnProperty('error_1') && errors['error_1'] )

The method hasOwnProperty can be used to determine whether an object has the specified property as a direct property of that object.

The errors[key] where key is a string value checks if the value exists and is not null

to Check if its not empty where it is a string then typeof errors['error_1'] === 'string' && errors['error_1'].length where you are checking for the length of a string

Result:

if (errors.hasOwnProperty('error_1') && typeof errors['error_1'] === 'string' && errors['error_1'].length)

Now, if you are using a library like underscore you can use a bunch of utility classes like _.isEmpty _.has(obj,key) and _.isString()

edited Feb 17, 2015 at 0:32

answered Feb 17, 2015 at 0:14

AhmadAssaf

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2 Comments

Phil Over a year ago

OP said "not empty" but this will also be true for 0 and null

AhmadAssaf Over a year ago

thanks @Phil just added a String length check if he likes to specifically checks for non empty string

Phil · Accepted Answer · 2015-02-17 00:18:18Z

3

To precisely answer your question (exists and not empty), and assuming you're not referring to empty arrays, you could use

typeof errors.error_1 === 'string' && errors.error_1.length

answered Feb 17, 2015 at 0:18

Phil

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2 Comments

Ronnie Smith Over a year ago

dayum, so just plain old .length returns true if it's > 0, else false? You sure you don't need length > 0?

Phil Over a year ago

@RonRoyston yes. In a boolean expression, 0 is falsy

Amr · Accepted Answer · 2015-02-17 01:44:19Z

3

Here is a another good answer I found and wanted to share (after modification to fit my needs):

if ("property_name" in object_name && object_name.property_name !== undefined){
   // code..
}

So if I wanted to apply this on my example, it will look like:

if ("error_1" in errors && errors.error_1 !== undefined){
   // code..
}

answered Feb 17, 2015 at 1:44

Amr

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1 Comment

AhmadAssaf Over a year ago

the in operator looks down the property chain, so it might return unwanted results depending on the structure. hasOwnProperty checks the specified property as a direct property of that object

Armen Nersisyan · Accepted Answer · 2019-07-16 08:40:09Z

-2

In order to check whether the object is empty or not use this code.

if (Object.keys(object_name).length > 0) {

  // Your code

}

answered Jul 16, 2019 at 8:40

Armen Nersisyan

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2 Comments

crisc2000 Over a year ago

your code check if the object itself is empty, not the object property

salouri Over a year ago

not what the question is about

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