How to replace a dynamically specified attribute in JS object

Question

The attribute(or the nested object) is selected dynamically based on conditions. It can be one of the 4 possibilities as follows:

var tempData = o.title ? o["properties"] || o["items"]["properties"] : o[k]["properties"] || o[k]["items"]["properties"];

Then I get this new data, I want to replace the above selected with.

var newData = //some new Object

I want to replace whatever above selected with the new data. I could do the following (go through the condition again and set the new data):

        if(o.title){
                if (o["properties"]) {
                    o["properties"] = newData;
                } else if (o["items"]["properties"]) {
                    o["items"]["properties"] = newData;
                }
        }else{
                if (o[k]["properties"]) {
                    o[k]["properties"] = newData;
                } else if (o[k]["items"]["properties"]) {
                    o[k]["items"]["properties"] = newData;
                }
        }

But it doesn't look good. What is the more sophisticated way of achieving this?

A better way would be to store the object you want to set properties on in tempData, and then do something like tempData.properties = newData;. To access the data, use tempData.properties instead of tempData (of course you should give tempData a better name). — Felix Kling
– Felix Kling, Commented Nov 2, 2016 at 5:52
Short answer no. Unless javascript support pointers, there is no simpler way. — user6360214
– user6360214, Commented Nov 2, 2016 at 5:52
All you've done with tempData is determine if one of the properties you are wanting to replace exists and evaluates to true. You did not actually save the one that you have found. — Makyen
– Makyen ♦, Commented Nov 2, 2016 at 6:07

Makyen · Accepted Answer · 2016-11-02 07:23:46Z

It is unclear if you are generically attempting to replace any properties property with the newData, or if you are wanting it to specifically be one of the ones you have specified in your code. I have assumed that you are only wanting to replace the ones you specifically have shown in your code.

Note: The following assumes that it is not possible for the value of the properties property to evaluate to false. If it is possible for it to have a value that evaluates to false, this will fail.

As a first pass, I would do something like:

var p;
if (o.title) {
    p=o;
} else {
    p=o[k];
}
if (p.properties) {
    p.properties = newData;
} else if (p.items.properties) {
    p.items.properties = newData;
}

However, that relies on:

o is not null or undefined.
o.title does not evaluate to false, if you are trying to test for the existence of o.title.
k is valid/defined.
p (i.e. o[k]) is not null or undefined (i.e. is an Object)
p.properties does not evaluate to false, if you are testing for existence
p.items is not null or undefined (i.e. is an Object)
p.items.properties does not evaluate to false, if you are testing for existence

A more robust implementation would be:

if (typeof o === 'object' && o !== null) {
    var p;
    if (o.hasOwnProperty('title')) {
        p = o;
    } else {
        p = o[k];
    }
    if (typeof p === 'object' && p !== null) {
        if (p.hasOwnProperty('properties')) {
            p.properties = newData;
        } else if (typeof p.items === 'object' && p.items !== null 
                   && p.items.hasOwnProperty('properties')) {
            p.items.properties = newData;
        }
    }
}

This still relies on:

k is valid/defined.

Basically, it is OK to use shortcuts like if(o.title) to test for existence, if you know that

the possible values for o can not include ones which might make your code throw an error (e.g o is null or undefined), and
the possible values for o.title do not evaluate to false when the property actually exists (e.g. o.title is null, undefined (yes, the property can exist, but have the value undefined), false, 0, '', etc.).

If you are going to perform the replacements in other areas of your code, or if you are going to use property keys other than hard coded items, and properties, then you should create a function. Assuming you are only performing this replacement in this section of your code, using a variable to hold the object in which you are looking for properties is faster/more efficient than creating a function.

@SachiDangalla, I have updated this answer with a more robust version of the code. It is not clear from your question if some of the checks you are doing in if statements are just to check for the existence of a property, or if you are aware you are also testing the property's value, in addition to testing for existence. Given that you don't know where in o the properties key may be, it seamed that you may not have much control over o and the code should account for possibly invalid values (or at least values for properties which might evaluate to false.

Hans Yulian · Accepted Answer · 2016-11-02 05:55:56Z

1

Ok, from what i can understand here, it's like you are trying to replace the "properties" with the new data, and you want this to be able to be done dynamically, or maybe i can say, you need to do this regardless the structure.

lets see, if your objective is anything that end up with "properties", lets do it like this:

function recReplace(current,target,replacement){
     for (var i in current){
          if (i == target){
                current[i] = replacement;
          }
          else{
               recReplace(current[i],target,replacement);
          }
     }
}

And in the end you call

recReplace(o,"properties",newData);

But this will replace whole "properties" key with newData in DFS way, you can do additional conditional if you want to replace it only the first occurence

answered Nov 2, 2016 at 5:55

Hans Yulian

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2 Comments

Mr_Green Over a year ago

I don't think it is good to loop all over the keys and also doing the recursive here. Compare to this OP's way is better.

Hans Yulian Over a year ago

Depends on what he needs, his requirement is vague... i try to understand what he is trying to do

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