Dynamically create sub-objects and arrays when needed

Question

I have an object created from JSON via AJAX from the server. The object has several sub-objects in an array, e.g.:

obj.subObj1[0].value="abc";
obj.subObj1[1].value="abc";
obj.subObj2[0].value="abc";

Now I want to set some values in this object but I dont know if they already exist.

obj.subObj1[0].value="new Value";  // No Problem
obj.subObj2[1].value="new Value2"; // Problem because obj.subObj2[1] is no Object.

I would need to do obj.subObj2[1]={} first.

Because I have this problem very often I am looking for method to automate this. A method or class which does automatically create the needed object (or array if I use an integer).

It should be able to handle an infinite depth of such sub-objects. Like this:

var obj = TheObject();
obj.sub1.sub2[10].sub3[1].sub4='value';

Now automatically all needed sub-objects and arrays should be created.

abelito · Accepted Answer · 2011-12-31 11:12:59Z

1

Cannot really guarantee anything about cross-browser compatibility, but how about trying this on for size (works in Chrome):

// Safely sets value property of index of an array of an object.
function setObj(obj, subObjName, index, val) {
    // Ensure the object exists
    if (typeof obj == 'undefined') {
        obj = new Object();
    }

    // Ensure the array property exists
    if (typeof obj[subObjName] == 'undefined') {
        obj[subObjName] = new Array();
    }

    // Ensure the array properties index exists
    if (typeof obj[subObjName][index] == 'undefined') {
        obj[subObjName][index] = {};
    }

    // Set the value
    obj[subObjName][index].value = val;

    // Return the object
    return obj;
}

Example use:

<script type="text/javascript">
    var obj;
    obj = setObj(obj, "something", 1, "val");
    setObj(obj, "something", 0, "someValue");
    alert(obj.something[1].value);
    alert(obj.something[0].value);
</script>

answered Dec 31, 2011 at 11:12

abelito

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2 Comments

Jascha Schubert Over a year ago

This works for the limit example. I am looking for a generic solution for unlimit depth in the objects. I also want to do obj.some[0].other[1].another.value and so on.

abelito Over a year ago

That's not really what you asked, but you can change your question a little to reflect that. In order to do something like that, I would imagine you would need a string parsing function to automagically create the appropriate object and array variables.. the resulting call would look something like this: parentObject = createBlueSmoke("obj.some[0].other[1].another.value", "some value");

nnnnnn · Accepted Answer · 2011-12-31 11:13:30Z

0

If you can assume that the referenced item in the array will be either undefined or an object it simplifies things. Of course the simple (non-automatic) way would be something like this:

if (!obj.subObj2[1]) obj.subObj2[1] = {};
obj.subObj2[1].value = "new Value2";

A not-very generic function to do it for you would be:

function setArrayObjectProp(arr, index, prop, val) {
   if (!arr[index])
       arr[index] = {};

   arr[index][prop] = val;
}

// called as
setArrayObjectProp(obj.subObj2, 1, "value", "new Value2");

answered Dec 31, 2011 at 11:13

nnnnnn

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Comments

Marwan · Accepted Answer · 2011-12-31 11:19:55Z

0

heloo

try testing the type of the array item first if its not object then equal it to the new object format {value:"new Value2"}

if(typeof(obj.subObj2[1])!='object')
{
obj.subObj2[1] = {value:"new Value2"};
}
else
{
obj.subObj2[1].value = "new Value2";
}

answered Dec 31, 2011 at 11:19

Marwan

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