Updating nested objects dynamically in javascript [duplicate]

Question

I have an object that is decoded from a json:

var data = [{
    "parentSeries":1,
    "children":[{
        "BusinessRule":"ChrisTest2",
        "ID":"ChrisTest2||3",
        "childsub":3,
        "jsonCondition":{
            "parentSeries":1,
             "children":[{
                 "RuleDefinition":"ChrisTest2||3",
                 "ID":"ChrisTest2||3||CondField1",
                 "Field":"CondField1",
                 "Test":"=1"
             },{
                 "RuleDefinition":"ChrisTest2||3",
                "ID":"ChrisTest2||3||CondField2",
                "Field":"CondField2",
                "Test":"=2"
             }]
        }
    }]
}]

I want to update any elements of this object dynamically. I have an array that shows me where the property I want to update is. eg:

var splitMap = ["jsonCondition", "children", "0", "Test"]

I have a value I want to update the final entry in this array with coming in (newValue), and I've got a bit of code to update the particular nested item to contain this new value:

if (splitMap.length > 0) {
    var newdata = data;
    for (var p = 0; p < splitMap.length-1; p++) {
        newdata = newdata[splitMap[p]];
    }
    newdata[splitMap[splitMap.length - 1]] = newValue;
}

But I can't figure out a way to get this updated into the original data! I basically want to do

oldobject['jsonCondition']['children'][0] = newdata

or

oldobject['jsonCondition']['children'][0]['Test'] = newValue

...but I want it work out the keys and depth of this path based on the content and length of the map array. I have jquery on our platform if that helps ($.each?)! Any ideas? Thanks :)

have you thought of writing a recursive function that uses $.each and checks to see if the next level down is an object? — josh123a123
– josh123a123, Commented Feb 26, 2015 at 18:27
where does splitMap array come from? Starting there you might be able to store an object reference that would make it even easier — charlietfl
– charlietfl, Commented Feb 26, 2015 at 18:28
Thanks all, I was able to use @Labithiotis answer on the duplicate question :) — chrisb
– chrisb, Commented Feb 27, 2015 at 16:45

Matt Burland · Accepted Answer · 2015-02-26 18:30:21Z

1

You should be able to just walk you way down your object by using the bracket notation [] to access each property in turn:

var curr = oldobject;   // this keeps track of our current position
for (var i=0; i < splitMap.length-1; i++) {
    if (curr.hasOwnProperty(splitMap[i]) {
        curr = curr[splitMap[i]];
    }
    else {
       // your map is wrong! Up to you how to handle this error
    }
}
curr[splitMap[i]] = newValue;    // for the last property, we set the value

answered Feb 26, 2015 at 18:30

Matt Burland

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2 Comments

chrisb Over a year ago

Thanks! That's pretty much where I got to (although your loop is better, thanks!).My issue is that this updates the lowest nested object, but I can't work out how merge that with the parent 'oldobject' object, in the right context, and via the splitMap array rather than hard-coding the object reference (because the splitMap array could be anything, and any depth). i.e., I want to do oldobject['jsonCondition']['children'][0] = curr, but I want it to be programmatic.

Matt Burland Over a year ago

@chrisb: Not sure what you mean. You are updating the property at the lowest level of the original object. There is no need to merge anything. That's why we only loop until the penultimate property if your splitMap. Because we want to assign to the very last one.

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