Access value from JavaScript object via array-string

Question

my problem is that i have a json-object with and array into here an example.

var object = {
 'items':['entry1','entry2']
}

I want to access 'entry2' over a constant string that I receive and shouldn't be changed.

var string = 'items[1]';

The only way I'm solving this problem is over the eval function...

eval('object.'+string);

This returns me entry2.

Is there any other way to achieve this without using eval()? Like object[string] or object.string

• Denys Séguret: What are the possible values of string ?
• marius: in this case 'items[0]' or 'items[1]'

Answer 1

Supposing your string is always the same form, you could extract its parts using a regex :

var m = string.match(/(\w+)\[(\d+)\]/);
var item = object[m[1]][+m[2]];

---

Explanation :

The regex builds two groups :

(\w+) : a string
\[(\d+)\] : some digits between brackets

and those groups are at index 1 and 2 of the array returned by match.

+something parses the number. It's not strictly needed here as the array accepts a string if it can be converted but I find the code more readable when this conversion is explicited.

• marius: this is the solution but I seem not to understand it correctly. Anyway it works and I have to check how the method is working. Thx :)
• marius: yeah, I've also found the method on google and it helped alot. Thx :)

Answer 2

On top of dystroy's anwser, you can use this function:

function getValueFromObject(object, key) {
 var m = key.match(/(\w+)\[(\d+)\]/);
 return object[m[1]][+m[2]];
}

Example:

var object = {
 'items':['entry1','entry2']
}
var string = 'items[1]';
var value = getValueFromObject(object, string); //=> "entry2"

• Denys Séguret: Does this really add something to my answer ?

Answer 3

First, you can get the array from inside:

var entries = object.items // entries now is ['entry1','entry2']

Then you need to index that to get the second item (in position 1). So you achieve what you want with:

var answer = entries[1] // answer is now 'entry2'

Of course, you can combine this to get both done in one step:

var answer = object.items[1] // answer is now 'entry2'

... I can see this is a contrived example, but please don't call your Objects 'object', or your Strings 'string' :s

• marius: it was just for the understanding ;) but I honor your advice

Answer 4

try something like this

 object.items[1];

• marius: this isnt possible since items[1] is received as a string... that's my problem...
• marius: as I told before items[1] is received as a string from an request so it's not static code. It's a string = 'items[1]'