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tslatt

How to tell if nested object exists?

in Using jQuery • 11 years ago

I have a nested object structured like this:

var wDefaults = {
"pcrPortal":{
"pcr001":{"wclosed":false,"wcollapsed":true,"pcol":0},
"pcr002":{"wclosed":false,"wcollapsed":true,"pcol":1},
"pcr003":{"wclosed":false,"wcollapsed":true,"pcol":2}
},
"pcfPortal":{
"pcf001":{"wclosed":false,"wcollapsed":true,"pcol":0},
"pcf002":{"wclosed":false,"wcollapsed":true,"pcol":1}
},
"posPortal":{
"pos001":{"wclosed":false,"wcollapsed":true,"pcol":0},
"pos002":{"wclosed":false,"wcollapsed":true,"pcol":1}
}
};

There can be more items in it than just "pcrPortal", "pcfPortal", and "posPortal".

How can I find out if a particular nested object exists in wDefaults? I have tried the following three methods, but I got "object is null or undefined" errors each time:

var pID = "pcfPortal";
if (wDefaults[pID].length) { /* it exists! */ }
if (wDefaults[pID] != undefined) { /* it exists! */ }
if (wDefaults[pID] != null) { /* it exists! */ }

Any help would be greatly appreciated!

Replies(4)

bvoyelr

Re: How to tell if nested object exists?

11 years ago

if(wDefaults.pcrPortal) {
// it exists
}

However,

if(wDefaults.bad.pcf001) {
}

will fail -- you have to nest your checks, like:

if(wDefaults.bad && wDefaults.bad.pfc001) {
// they both exist
}

sheldon.g..

Re: How to tell if nested object exists?

11 years ago

The safe way to check whether something exists or not is using "typeof ... 'undefined'" - in your case:

if (typeof wDefaults[pID] != "undefined")

(As an aside, though I'm sure you know it already, and just included it as an attempt to test for existince, even though the items are clearly - to our eyes - lists, .length isn't going to work even when the nested object does exist, because to JavaScript's eyes, they're objects, not arrays)