How to access property of a nested object?

Question

I have the following Javascript object:

doc = {};
doc.title = 'a title';
doc.date = 'a date';
doc.send = {
    date: new Date(),
    sender: 'a sender',
    receiver: 'a receiver'
};

And i have the following function:

doSomething(item, property) {
    console.log(item[property];
}

It works if i call doSomething(doc, 'date'), but it doesn't work if i use doSomething(doc, 'send.date'). Since that function have to be reusable, how to let it handling any type of property, including nested one?

I see that lodash could be helpful with _.get, but i'm using underscore that not include that method. In addition i prefer not to use and install other libraries. Any idea?

Dup? http://stackoverflow.com/questions/2631001/javascript-test-for-existence-of-nested-object-key — elclanrs, Mar 25 '16 at 16:10
@elclanrs The question you linked is about checking for existence, and this one is about accessing. — Michał Perłakowski, Mar 25 '16 at 16:11
Pretty much the same thing, if you can access it then it exists... — elclanrs, Mar 25 '16 at 16:14

score 0 · Answer 1 · edited Mar 25 '16 at 16:16

0

You can write a function to find (nested) property value, for example:

function findDeepProp(obj, prop) {
    return prop.split('.').reduce((r, p)=> r[p], obj)
}
findDeepProp(doc, 'title'); // a title
findDeepProp(doc, 'send.sender'); // a sender

edited Mar 25 '16 at 16:16

Michał Perłakowski

88,409
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answered Mar 25 '16 at 16:12

madox2

49,493
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1

This will throw an error on nested properties that don't exist. – elclanrs Mar 25 '16 at 16:15
And it only works on one level of nesting. May or may not be important. – Andy Mar 25 '16 at 16:16
@elclanrs sure, why not to throw when trying to access properties of `undefined`? This is just how javascript works – madox2 Mar 25 '16 at 16:21
I would avoid exceptions. All you need is `.reduce((r, p) => r && r[p], obj)` – elclanrs Mar 25 '16 at 16:25

score 0 · Answer 2 · answered Mar 25 '16 at 16:27

0

This is a bit dangerous depending on what you're trying to do, I recommend you to read this, but I think this will work:

doSomething = function(element, property){
    console.log(eval("element." + property));
}

answered Mar 25 '16 at 16:27

GBarroso

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8
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Andy · Answer 3 · 2016-03-25T17:15:55.263

If you wanted to check more than one level of nesting you could use a function that uses recursion.

var doc = {
  title: 'a title', date: 'a date',
  send: { date: +new Date(), sender: 'a sender', receiver: 'a receiver',
    thing: {
      fullname: { first: 'Bob', last: 'Smith' }
    }
  }
}

function findDeepProp(obj, prop) {

  // create an array from the props argument
  var target = prop.split('.'), out;

  // iteration function accepts an object and target array
  (function iterate(obj, target) {

    // remove the first array element and assign it to tmp
    var tmp = target.shift();

    // if target has no more elements and tmp
    // exists as a key in the object passed into iterate()
    // return its value
    if (target.length === 0 && obj[tmp]) return out = obj[tmp];

    // if the key exists in the object passed into iterate()
    // but it is an object, run iterate() with that object
    // and the reduced target array
    if (obj[tmp] && typeof obj[tmp] === 'object') iterate(obj[tmp], target);

    return;
  }(obj, target));

  return out;
}

findDeepProp(doc, 'send.thing.fullname.first') // Bob
findDeepProp(doc, 'send.thing.fullname.last') // Smith

DEMO

How to access property of a nested object?

3 Answers3