How to convert chained property from string into a variable from javascript

Question

I have this variable that is stored in a string

  var employee  = {
        name: 'person',
        job: {
           post: 'developer',
           since: 2010,
           desk: {
              number: '1',
        }
    }
  };

How can i get the keychain value from a string e.g.

  var variable = "job.desk.number";
  console.log(variable);
  //this should return 1

UPDATE 3 !!

@T.J. Crowder's answer is actually the best answer.

His function is quick and tidy. :) horry!

See here: http://stackoverflow.com/questions/45015/safely-turning-a-json-string-into-an-object — twh, Feb 17 '15 at 08:34
Nope json.parse will not work as I have "job.desk.number" as a string and i want to turn it into a value. Please understand the question before answering thanks! — Mhammad Chehab, Feb 17 '15 at 08:36
Template! i have an html template where these strings are actually ${module.label.something} and based on the language I return the value. — Mhammad Chehab, Feb 17 '15 at 08:55

T.J. Crowder · Accepted Answer · 2015-02-17T08:42:02.170

Split the string so you have an array of keys, then loop through them getting each key in turn from the object, remembering the last thing you got from the object:

var value = variable.split('.').reduce(function(prev, key) {
  return prev[key];
}, employee);
snippet.log(value);

Example:

var employee  = {
  name: 'person',
  job: {
    post: 'developer',
    since: 2010,
    desk: {
      number: '1',
    }
  }
};

var variable = "job.desk.number";
var value = variable.split('.').reduce(function(prev, key) {
  return prev[key];
}, employee);
snippet.log(value);

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

Note that Array#reduce is an ES5 thing, so it's in all modern browsers but not some older ones. It can be shimmed/polyfilled, though. Or if you just prefer to use a for loop:

var keys = variable.split('.');
var value = employee;
var index;
for (index = 0; index < keys.length; ++index) {
    value = value[keys[index]];
}
snippet.log(value);

Example:

var employee  = {
  name: 'person',
  job: {
    post: 'developer',
    since: 2010,
    desk: {
      number: '1',
    }
  }
};

var variable = "job.desk.number";
var keys = variable.split('.');
var value = employee;
var index;
for (index = 0; index < keys.length; ++index) {
    value = value[keys[index]];
}
snippet.log(value);

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

score 0 · Answer 2 · answered Feb 17 '15 at 08:37

Lets say for example your variable emplyee is like

var employee = "{ name: 'person', job: { post: 'developer', since: 2010, desk: { number: '1', } } }";

which is in fact a string then you need to parse it to JSON using JSON.parse(employee)

And you can access your variable like

var variable = employee.job.desk.number

Alternative to your case is :

var variable = "" + employee.job.desk.number;

Mhammad Chehab · Answer 3 · 2015-02-17T09:36:23.483

0

The result is actually working however i wonder about performance.

 var _getKeyChainValueFromObject = function (keychain, root) {
    var items = [];
    if (keychain.indexOf(".") > 0)
        items = keychain.split(".");
    else
        return root[keychain];

    for (var i = 0; i < items.length ; i++) {
        for (var property in root) {
            var key = items[i];
            if (property === key) {
                if (typeof (root[property]) === "object") {
                    var scope = root[property];
                    items.splice(0, 1);
                    //get the resource recursively 
                    return _getKeyChainValueFromObject(items.join('.'), scope);
                }
            }
        }
    }
};

edited Feb 17 '15 at 09:36

answered Feb 17 '15 at 08:37

Mhammad Chehab

93
8

It can be a lot simpler than that. :-) – T.J. Crowder Feb 17 '15 at 08:39
yes I marked your answer @T.J.Crowder as the correct one as mine is a bit messy. – Mhammad Chehab Feb 17 '15 at 08:49

score 0 · Answer 4 · answered Nov 23 '22 at 15:50

I've found a better solution that works with objects and arrays of objects.

const userObject = {
  user: {
    name: "Victor",
    posts: [
      {
        title: "Post #1",
        description: "........"
      },
      {
        title: "Post #2",
        description: "........"
      }
    ]
  }
};

const path = "user.posts[0].title";

const valueByPath = path.match(/\d+|\w+/gm).reduce(function (prev, key) {
  return prev[key];
}, userObject);

console.log(valueByPath);

How to convert chained property from string into a variable from javascript

4 Answers4