Convert string to an attribute for a nested object in javascript

Question

I am trying to access a string "key1.key2" as properties of an object. For example :

var obj = { key1 : {key2 : "value1", key3 : "value2"}};
var attr_string = "key1.key2";

The variable attr_string is a string of attributes in a nested object joined by ".". It can be of any depth like "key1.key2.key3.key4..."

I want something like obj.attr_string to give the value of obj["key1"]["key2"] that is "value1"

How to achieve this?

A combination of two anti-patterns: `with (obj) var result = eval(attr);`. — dfsq, Feb 21 '13 at 12:31
possible duplicate of [Accessing nested JavaScript objects with string key](http://stackoverflow.com/questions/6491463/accessing-nested-javascript-objects-with-string-key) — Felix Kling, Feb 21 '13 at 12:35
Please read: ['There is no such thing as a "JSON object"'](http://benalman.com/news/2010/03/theres-no-such-thing-as-a-json/). What you have is a normal JavaScript object. — Felix Kling, Feb 21 '13 at 12:36
@dfsq I dont get it. `eval(attr)` will give "Reference Error for key1" Can you please explain more clearly? — Manu K Mohan, Feb 21 '13 at 12:37
I say it again: What you have is **not** JSON. I won't start an edit war though. — Felix Kling, Feb 21 '13 at 12:45
@dfsq `eval(attr_string)` gives "Reference Error for key1" . — Manu K Mohan, Feb 21 '13 at 12:48
And note that using `with` will throw an error in strict mode. I wouldn't recommend using it. Have a look at the question I linked to, it contains the solution you seek. — Felix Kling, Feb 21 '13 at 12:51

score 3 · Accepted Answer · edited Jun 01 '22 at 15:58

3

Thanks @dfsq for remembering me the use of eval.

Here is what I was expecting, a simple way to evaluate the objects string attribute.

var obj = { key1 : {key2 : "value1", key3 : "value2"}};
var attr_string = "key1.key2";

var result = eval("obj."+attr_string);

There is no need of splitting the string with "." and then putting it in a loop to get the value. eval can evaluate any string with javascript code statement.

Be noted: although the code functions as expected, eval should not be used!!!

see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval#never_use_eval!.

edited Jun 01 '22 at 15:58

Roi Shabtai

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answered Feb 21 '13 at 13:32

Manu K Mohan

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NEVER USE EVAL!!! https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval#never_use_eval! – Roi Shabtai Jun 01 '22 at 15:58

score 0 · Answer 2 · edited Jun 01 '22 at 16:25

0

var target = obj;
const parts = attr_string.split(".");
for (var part in parts)
  target = target[part[part]];

edited Jun 01 '22 at 16:25

Roi Shabtai

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answered Feb 21 '13 at 12:24

John Zwinck

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score 0 · Answer 3 · answered Feb 21 '13 at 12:52

Is this what you are after?

var obj = { key1: { key2A: 'x', key2B: { key3: 'y' } } },
    attr_string = 'key1.key2B.key3',

    find = function ( obj, str ) {

        var index = 0,
            arr = str.split( '.' );

        if ( arr.length ) {
            while ( typeof obj === 'object' &&  arr[ index ] in obj ) {
                obj = obj[ arr[ index ] ];
                index++;
            }
        }

        return obj;

    };


find( obj, attr_string ); // Returns 'y'

score 0 · Answer 4 · answered Feb 05 '14 at 10:00

fixing up @John's answer into a re-usable function (which I will be using myself)

function nested(obj, attrString){
    var path = attrString.split(".");
    for (var i in path){
        obj = obj[path[i]];
    }
    return obj;
}

// test it out...
x = {a:{b:{c:"happy days"}}};
console.log(nested(x, 'a'));
console.log(nested(x, 'a.b'));
console.log(nested(x, 'a.b.c'));

Convert string to an attribute for a nested object in javascript

4 Answers4

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