JavaScript check if property defined

Question

What is the recommended way to check if an object property like obj.prop.otherprop.another is defined?

if(obj && obj.prop && obj.prop.otherprop && obj.prop.otherprop.another)

this works well, but enough ugly.

http://stackoverflow.com/questions/135448/how-do-i-check-to-see-if-an-object-has-a-property-in-javascript — JonH, Feb 15 '13 at 17:52

score 3 · Accepted Answer · answered Feb 15 '13 at 18:13

3

The most efficient way to do it is by checking for obj.prop.otherprop.another in a try{} catch(exception){} block. That would be the fastest if all the remaining exist; else the exception would be handled.

var a = null;
try {
  a = obj.prop.otherprop.another;
} catch(e) {
  obj = obj || {};
  obj.prop = obj.prop || {};
  obj.prop.otherprop = obj.prop.otherprop || {};
  obj.prop.otherprop.another = {};
  a = obj.prop.otherprop.another ;
}

answered Feb 15 '13 at 18:13

jagzviruz

1,283
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Please don't use this.. this is just stupid of me to suggest this. – jagzviruz Oct 13 '15 at 08:39

broofa · Answer 2 · 2013-02-15T17:56:24.190

0

Not saying this is better but ...

x = null
try {
  x = obj.prop.otherprop.another;
} catch() {}
// ...

Or alternatively ...

function resolve(obj, path) {
  path = path.split('.');
  while (path.length && obj) obj = obj[path.shift()];
  return obj;
}

x = resolve(obj, 'prop.otherprop.another');

... but I guess the actual answer is that there isn't a best-practice for this. Not that I'm aware of.

edited Feb 15 '13 at 17:56

answered Feb 15 '13 at 17:51

broofa

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73

score 0 · Answer 3 · answered Feb 15 '13 at 18:01

0

If you're in a silly mood, this would work:

if ((((obj || {}).prop || {}).anotherprop || {}).another) { ... }

But I don't know if initializing three new objects is really worth not having to repeatedly type out the path.

answered Feb 15 '13 at 18:01

Bubbles

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JavaScript check if property defined

3 Answers3