JS: Prevent Error if Accessing Attributes of Undefined Object

Question

My goal: Test if the attribute of an object is/returns true. However, in some cases, the object is undefined.

This works no problem. The script continues normally.

if(somethingUndefined){ }

However, if I try to access an attribute of an undefined object, this generates an error and stops the script.

if(somethingUndefined.anAttribute){ }

Right now, this is what I'm using to solve the problem:

if(somethingUndefined && somethingUndefined.anAttribute){ }

Is there another way to do that? Maybe a global settings that will return false if the program tries to access an attribute of an undefined object?

somethingUndefined && somethingUndefined.anAttribute is a standard practice — zerkms
– zerkms, Commented Sep 3, 2013 at 3:39
I'd love it if we could check nested properties without getting fatal errors. Working with the WP API atm and my code looks like this all over the place; if (this.post.featured_image && this.post.featured_image.media_details && this.post.featured_image.media_details.sizes && this.post.featured_image.media_details.sizes.large) — powerbuoy
– powerbuoy, Commented Sep 22, 2017 at 10:50

xdazz · Accepted Answer · 2013-09-03 03:43:58Z

1

If you have many if statement like if(somethingUndefined && somethingUndefined.anAttribute){ }, then you could assign an empty object to it when it is undefined.

var somethingUndefined = somethingUndefined || {};

if (somethingUndefined.anAttribute) {

}

answered Sep 3, 2013 at 3:43

xdazz

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Comments

Brandon J. Boone · Accepted Answer · 2013-09-03 04:09:01Z

1

You can take advantage of JavaScript's ability to assign variables within if conditions and follow this pattern for faster checks once you get past the first nested object.

JsPerf

var x; 
if(
   (x = somethingUndefined) && // somethingUndefined exists?
   (x = x.anAttribute) && // x and anAttribute exists?
   (x = x.subAttrubute) // x and subAttrubute exists?
){

}

vs the traditional

if(
    somethingUndefined && // somethingUndefined exists?
    somethingUndefined.anAttribute && // somethingUndefined and anAttribute exists?
    somethingUndefined.anAttribute.subAttribute // somethingUndefined and anAttribute and subAttribute exists?
){

}

answered Sep 3, 2013 at 4:09

Brandon J. Boone

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Comments

Jeff Escalante · Accepted Answer · 2013-09-03 03:49:16Z

0

The way you have it in your question is generally the way it's done in javascript. If you find yourself using this a lot, you could abstract it out into a function to make things a tiny bit cleaner for yourself, as such:

if (attrDefined(obj, 'property')) {
  console.log('it is defined, whoo!');
}

function attrDefined(o, p){ return !!(o && o[p]) }

answered Sep 3, 2013 at 3:49

Jeff Escalante

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