Updating Javascript object recursively

Question

I have an nested object that I want to update it with values provided by object that contains similar structure but only the properties that I want updated. Creating a new result instead of modifying the initial objects is great too.

    var initial = 
      { 
         a: 1, 
         b : { 
            c : 2, 
            d : 3 
         },
         f: 5 
      }; 

    var update = {
        a: 2,
        b: {
           d: 2
        }
    };         
    function updateFunction (a,b) {  return a+b;};
    var result= 
      { 
         a: 3, // updateFunction (1,2)=> 3
         b : { 
            c : 2, 
            d :5 // updateFunction (3,2) => 5
         },
         f: 5 
      };

Just iterate through properties, if typeof x == 'object' perform recursive call, otherwise compare and assign value if !== ... What kind of issue is there here ? What have you tried ? — GameAlchemist
– GameAlchemist, Commented May 5, 2013 at 12:16
The issue was that I thought that objects are passed by value instead of by reference. — slobodan.blazeski
– slobodan.blazeski, Commented May 5, 2013 at 12:52

shakib · Accepted Answer · 2013-05-05 13:25:16Z

5

Have not tested fully, but maybe,

assuming objects are simple as stated,

function updateFunction (a,b) {  return a + b;};    

function recurse(initial, update){
    for(prop in initial){
        if({}.hasOwnProperty.call(initial, prop) && {}.hasOwnProperty.call(update, prop)){
            if(typeof initial[prop] === 'object' && typeof update[prop] === 'object'){
                recurse(initial[prop], update[prop]);
            }
            else{
                initial[prop] = updateFunction(initial[prop], update[prop]);
            }
        }
    }
}
recurse(initial, update);

EDIT

If result is expected without changing initial

function updateFunction (a,b) {  return a + b;};

function recurse(initial, update){
    var result = {};
    for(prop in initial){
        if({}.hasOwnProperty.call(initial, prop)){
            result[prop] = initial[prop];    
            if({}.hasOwnProperty.call(update, prop)){
                if(typeof initial[prop] === 'object' && typeof update[prop] === 'object'){
                    result[prop] = recurse(initial[prop], update[prop]);
                }
                else{
                    result[prop] = updateFunction(initial[prop], update[prop]);
                }
            }
        }    
    }
    return result;
}
var result = recurse(initial, update);

hope this helps.

edited May 5, 2013 at 13:25

answered May 5, 2013 at 12:16

shakib

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7 Comments

Eric Over a year ago

Don't forget hasOwnProperty

Eric Over a year ago

initial.hasOwnProperty(prop) doesn't cut it - what if one of the keys in my object is hasOwnProperty? You need to use {}.hasOwnProperty.call(initial, prop), as in my answer

slobodan.blazeski Over a year ago

Thanks shakib it works great from my needs. I've changed only initial.hasOwnProperty(prop) to {}.hasOwnProperty.call(initial, prop) as per Eric suggestion.

shakib Over a year ago

@user1851442 You are welcome. edited the answer with the change.

Eric Over a year ago

Note that this modifies the original object, whereas mine creates a copy of the parts it changes.

|

Eric · Accepted Answer · 2013-05-05 12:42:42Z

3

Here's how I'd do it:

// The parallel to Array.map
Object.map = function(obj, f) {
    var result = {};
    for(k in obj)
        if({}.hasOwnProperty.call(obj, k))
            result[k] = f(k, obj[k]);
    return result;
}

// Takes two objects and uses `resolve` to merge them
function merge(a, b, resolve) {
    return Object.map(a, function(k, a_value) {
        if(k in b)
            return resolve(a_value, b[k]);
        else
            return a_value;
    });
}

// same as above, but recursing when an object is found
function recursive_merge(a, b, resolve) {
    return merge(a, b, function(a_value, b_value) {
        if(typeof a_value == 'object' && typeof b_value == 'object')
            return recursive_merge(a_value, b_value, resolve);
        else
            return resolve(a_value, b_value);
    });
}

result = recursive_merge(initial, update, function(a, b) { return a + b; })

edited May 5, 2013 at 12:42

answered May 5, 2013 at 12:20

Eric

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4 Comments

Bergi Over a year ago

Nice! Only you might consider cloning a_value objects even if they have no respective property in b - of course, that depends on the OPs exact needs.

Eric Over a year ago

@Bergi: I see what you mean

slobodan.blazeski Over a year ago

I can't run your code rmerge is not defined, throws error at result = rmerge(initial, update, function(a, b) { return a + b; }) ReferenceError: rmerge is not defined result = merge(initial, update, function(a, b) { return a + b; }) ReferenceError: v is not defined result = recursive_merge(initial, update, function(a, b) { return a + b; })

Eric Over a year ago

@user1851442: Whoops - fixed

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