How do I fix this simple Javascript 'for loop'?

Question

I have a number of Javascript objects.

I want a simple 'for loop' (in JS) that prints out the key:value pairs within each object.

I've shown what I've done below (and here it is in a FIDDLE), but the variable 'thisvar' isn't working.

I'm obviously missing something really simple - can you point out what it is?

Thanks

// declare objects
var variant1 = {};
var variant2 = {};

variant1['a'] = 'apple';
variant1['b'] = 'orange';
variant1['c'] = 'pear';

variant2['a'] = 'red';
variant2['b'] = 'green';
variant2['c'] = 'blue';

// run through each object
for (i=1; i<3; i++){
    var thisvar = variant+i;
    for(var newindex in thisvar) {
        var name = newindex;
        var contents = thisvar[newindex];
        alert(name+'='+contents);
    }
}

var thisvar = variant+i; you cannot create dynamic variables like that. — Felix Kling
– Felix Kling, Commented Nov 23, 2012 at 9:22

score 3 · Accepted Answer · 2012-11-23 09:38:42Z

3

// declare objects
var container = {
    variant1: {}
    variant2: {}
}

container.variant1['a'] = 'apple';
container.variant1['b'] = 'orange';
container.variant1['c'] = 'pear';

container.variant2['a'] = 'red';
container.variant2['b'] = 'green';
container.variant2['c'] = 'blue';

// run through each object
for (var i = 1; i < 3; i++){
    for (prop in container["variant"+i]){
         if (variant.hasOwnProperty(prop)){
            alert(prop+'='+var[prop]);
         }
    }
}

As pointed out in the comments below, if you want to numerically iterate over the properties, you're better off just using an array:

// declare objects
var variants = [{},{}];

variants[0]['a'] = 'apple';
variants[0]['b'] = 'orange';
variants[0]['c'] = 'pear';

variants[1]['a'] = 'red';
variants[1]['b'] = 'green';
variants[1]['c'] = 'blue';

// run through each object
for (var i = 0; i < 2; i++){
    for (prop in variants[i]){
         if (variant.hasOwnProperty(prop)){
            alert(prop+'='+var[prop]);
         }
    }
}

edited Nov 23, 2012 at 9:38

answered Nov 23, 2012 at 9:22

user1726343

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5 Comments

Felix Kling Over a year ago

Only works with global variables, just sayin'. OP is better off using an array of objects.

user1726343 Over a year ago

@FelixKling I'm assuming you meant object map of objects. Fixed my answer.

Felix Kling Over a year ago

No, I actually really meant array of objects... the "variantX" keys just seem to be a numeration, which arrays provide natively (kind of). But then again, there are multiple solutions for a problem :)

Steve Over a year ago

But I'd read in many places "Don't store key-value pairs in Arrays" (in objects instead) - phabricator.com/docs/phabricator/article/…

Felix Kling Over a year ago

@Steve: Well, not string keys, but numerical, consecutive keys (indexes) are fine. That's what makes an array an array.

Akhil Sekharan · Accepted Answer · 2012-11-23 09:23:14Z

1

Try this:

var variant1 = new Object();
variant1['a'] = 'apple';
variant1['b'] = 'orange';
variant1['c'] = 'pear';
var variant2 = new Object();
variant2['a'] = 'red';
variant2['b'] = 'green';
variant2['c'] = 'blue';


for (i=1; i<3; i++){
var thisvar ;
eval( 'thisvar = variant'+i);
    for(var newindex in thisvar) {
        var name = newindex;
        var contents = thisvar[newindex];
        alert(name+'='+contents);
    }
}

answered Nov 23, 2012 at 9:23

Akhil Sekharan

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1 Comment

user1726343 Over a year ago

Please avoid the use of eval.

August Karlstrom · Accepted Answer · 2012-11-23 09:34:34Z

1

If you just want to inspect the object properties you can simply do

alert(JSON.stringify(container))

answered Nov 23, 2012 at 9:34

August Karlstrom

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