Javascript中的变量“变量” - 未定义

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?

Answer 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": {}

Answer 2

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]]] = ...

Answer 3

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 
    });

}