Variable "Variables" in Javascript - Undefined

Question

JSON:

var promiseObj = {
"physical": [],
"virtual": []
}
var config = {
"Environments": [
"LH5",
"LH8",
"AMS"
],
 "Clusters": {
    "LH5": 4,
    "LH8": 4,
    "AMS": 4
}
};

So I am trying to set different promise objects based on the environments and the clusters in the given JSON object above.

for (var i = 0; i < config.Environments.length; i++) { 
    promiseObj.physical[config.Environments[i]][config.Clusters[config.Environments[i]]] = $http.get('URL').success(function(data) {
    //Successful stuff here 
});

}

However when performing this for loop I get the following error:

promiseObj.physical[config.Environments[i]] is undefined

Could someone shed some light into why this is returning undefined, when the object is clearly defined at the start of the document?

promiseObj.physical = []; therefore promiseObj.physical[anything] will be undefined. It doesn't matter what config.Environments[i] returns because the physical array is empty. — Corey Ogburn
– Corey Ogburn, Commented Sep 1, 2015 at 14:56
Since config.Environments[i] is a string, promiseObj.physical[string] has wrong syntax (array index cannot be a string — hindmost
– hindmost, Commented Sep 1, 2015 at 14:59
I would first break that long expression into shorter expressions using local variables. Eg var envname = config.Environments[i]; instead of repeating that expression. It makes it easier to read. Then double-check that you really want the multiple levels of nesting in the data structure that the code expects (but currently fails because you can't index undefined). — dsh
– dsh, Commented Sep 1, 2015 at 15:00

deceze · Accepted Answer · 2015-09-01 14:59:42Z

1

Since physical is an empty array, any and all keys within it are undefined. You need to prime them the first time you use them:

if (typeof promiseObj.physical[config.Environments[i]] == 'undefined') {
    promiseObj.physical[config.Environments[i]] = {};  // or [], whichever you want
}
promiseObj.physical[config.Environments[i]][config.Clusters[config.Environments[i]]] = ...

answered Sep 1, 2015 at 14:59

deceze♦

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LostMyGlasses · Accepted Answer · 2015-09-01 14:59:27Z

1

You're declaring physical as an array and then accessing it as an object, so you're trying to access a property that can't exist. Try declaring physical as follows:

"physical": {}

answered Sep 1, 2015 at 14:59

LostMyGlasses

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nanndoj · Accepted Answer · 2015-09-01 15:00:08Z

1

This is because promiseObj.physical[] is an empty array, you have to initialize the index you want before:

for (var i = 0; i < config.Environments.length; i++) { 
    if(!promiseObj.physical[config.Environments[i]]) promiseObj.physical[config.Environments[i]] = {}; // Initialize it
    promiseObj.physical[config.Environments[i]][config.Clusters[config.Environments[i]]] = $http.get('URL').success(function(data) {
    //Successful stuff here 
    });

}

answered Sep 1, 2015 at 15:00

nanndoj

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