Merging two object in javascript

Question

I having the following code to merge the two objects

Code:

var goals = {1:"first",2:"second"};
var pages = {1:"page1",2:"page2"};

var result = {};

for(var goal in goals){
  for(var page in pages){
       if(page.hasOwnProperty(goal)){
         result[goal] = {"goal":goals[goal],"page":pages[page]};
      }
  }
}

console.log(result);

Expected result:

result = {1:{"goal":"first","page":"page1"},2:{"goal":"second","page":"page2"}};

code is working fine and getting the expected output.

Any suggestion to change it or it is better to go with this.

Improved code

    var result = {};

    for(var goal in goals){
     if(pages.hasOwnProperty(goal)){
        result[goal] = {"goal":goals[goal],"page":pages[goal]};
      }
    }

if pages has more properties then it will not show up in your output. Will this scenario happen? — eggward
– eggward, Commented Oct 24, 2013 at 13:03

Akshaya Shanbhogue · Accepted Answer · 2013-10-24 13:02:50Z

1

Your solution is O(m*n). The following is of O(m+n):

var goals = {1:"first",2:"second"};
var pages = {1:"page1",2:"page2"};

var result = {};
for(var x in goals){
if(!result[x])result[x] = {};
result[x].goals = goals[x];
}
for(var x in pages){
if(!result[x])result[x] = {};
result[x]. page = pages[x];
}

answered Oct 24, 2013 at 13:02

Akshaya Shanbhogue

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1 Comment

Elias Van Ootegem Over a year ago

Could be more efficient & complete still: while looping over one object, check if those keys exist in the second. Delete the property if it does, after adding it to the result, of course (cf my answer). You're also not filtering (hasOwnProperty) the loop. It's redundant 9/10 cases, true, but you never know how the OP is going to use your code

subZero · Accepted Answer · 2013-10-24 13:03:48Z

1

With Underscore.js you get a nice and simple one-liner:

var result = _.extend(goals, pages);

answered Oct 24, 2013 at 13:03

subZero

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1 Comment

fray88 Over a year ago

I highly recommend underscore as well

lukas.pukenis · Accepted Answer · 2013-10-24 13:02:07Z

0

You need to use obj.hasOwnProperty().

When you do for x in y it provides you all the properties and methods of an object.

obj.hasOwnProperty() tells you if a property is a direct property on the object or in it's prototype(if returns false).

Your extend function should look like this:

function extend(src, dst){
    for(var key in dst)
        if(dst.hasOwnProperty(key))
            src[key] = dst[key];
    return src;

answered Oct 24, 2013 at 13:02

lukas.pukenis

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