build objects in for loop with javascript

Question

I am trying to dynamically build an object for every iteration of a for loop using the i as part of the object name. based on the example below I would like 19 objects with names: obj0, obj1, obj2... obj18.

so I have an array with a length:

    console.log(foo.length); // 19

    for (var i = 0; i < foo.length; i++) {
        var bar+i  = {}; 
    };
    console.log(bar1);
    console.log(bar2);
    // ...
    console.log(bar18);

I can't figure out the correct syntax for "var bar+i = {};", obviously it does not work.

EDIT I really need objects because I am constructing data to be used in D3.js that needs to be an array of many objects

Is there any reason these need to be global? Or not in an array? — woolstar
– woolstar, Commented Dec 13, 2013 at 15:03

David Barker · Accepted Answer · 2013-12-13 15:09:29Z

2

Unless bar{i} is an array value / object property itself the only way to do this is to bind it to the window or root object.

window[bar+i] = {};

Or to the root object

this[bar+i] = {};

Much better to bind it to an array / object itself though rather than bind senselessly to the root/window.

var array = [];

array[bar+i] = {};

edited Dec 13, 2013 at 15:09

answered Dec 13, 2013 at 15:04

David Barker

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1 Comment

Bwyss Over a year ago

Binding to an array is just what I needed to do, your third comment did just the trick, with one small change: array["bar"+i] = {};

RononDex · Accepted Answer · 2013-12-13 15:04:12Z

2

There are some hacks how you can achieve this. However I advice you to use arrays instead of that method you are trying to use:

 console.log(foo.length); // 19

 var variables = [];

 for (var i = 0; i < foo.length; i++) {
    variables[i]  = {}; 
 };
 console.log(variables[0]);
 console.log(variables[1]);
 // ...
 console.log(variables[18]);

answered Dec 13, 2013 at 15:04

RononDex

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2 Comments

MJC Over a year ago

He doesn't have to use arrays. He can use an object instead... but yeah.. the rest is correct.

Pavlo Over a year ago

Creating an array from literal ([]) is faster then new Array().

Sirko · Accepted Answer · 2013-12-13 15:04:51Z

2

You can't create variables like this.

What you can do is add properties of the global scope, which you can use as variables:

for (var i = 0; i < foo.length; i++) {
  window['bar'+i ] = {}; 
};

or use another object to hold everything:

var container = {};
for (var i = 0; i < foo.length; i++) {
  container['bar'+i] = {}; 
};

answered Dec 13, 2013 at 15:04

Sirko

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Comments

Barney · Accepted Answer · 2013-12-13 15:07:48Z

1

You can't dynamically write variable names, but you can do the same on object properties:

console.log(foo.length); // 19

var obj = {};

for (var i = 0; i < foo.length; i++) {
    obj[ 'bar' + i ] = {}; 
};

console.log(obj.bar1);
console.log(obj.bar2);
// ...
console.log(obj.bar18);

answered Dec 13, 2013 at 15:07

Barney

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Comments

pvgoran · Accepted Answer · 2013-12-13 15:05:24Z

0

You can use eval:

eval('var bar'+i+' = {};');

But really, you shouldn't be doing this, unless you know for sure you can't do it the other way.

answered Dec 13, 2013 at 15:05

pvgoran

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2 Comments

Pointy Over a year ago

This answer is correct, but it's kind-of like, "Well, you can do it by putting on the One Ring of Power, but please don't because MORDOR."

pvgoran Over a year ago

@Pointy Because MORDOR will get you?

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