In javascript how can I dynamically get a nested property of an object

Question

var arr = { foo : 1, bar: { baz : 2 }, bee : 3 }

function getter(variable) {
  return arr[variable];
}

If I want 'foo' vs 'bee' I can just do arr[variable] - that's easy, and the function does that.

But what if I want to get arr.bar.baz AKA arr[bar][baz]?

What can I pass to the getter function that will let me do that, (and of course also let me get non-nested properties using the same function).

I tried getter('bar.baz') and getter('[bar][baz]') but those didn't work.

I suppose I can parse for dots or brackets (like here: In javascript, test for property deeply nested in object graph?). Is there a cleaner way? (Besides eval of course.)

Especially because I need to get the deeply set properly many many times in a loop for a bunch of array elements.

Why don't you just use that approach from the linked question? — Shi, Aug 02 '11 at 00:50
Mainly because of the overhead of calling the function so often, and also if there is a better way I want to learn it. — Ariel, Aug 02 '11 at 00:53
another option is to reference a callback as the variable argument, like this: getter(obj => obj.foo.bar.baz) then you call it inside your algorithm getter(variable) { return variable(arr) } maybe test if is a string and just use the [ ] notation or if it is function call it. — João Melo, Apr 01 '21 at 17:07

RobG · Answer 1 · 2021-09-29T21:35:51.207

58

You can use a deep access function based on a string for the path. Note that you can't have any periods in the property names.

function getPropByString(obj, propString) {
  if (!propString)
    return obj;

  var prop, props = propString.split('.');

  for (var i = 0, iLen = props.length - 1; i < iLen; i++) {
    prop = props[i];

    var candidate = obj[prop];
    if (candidate !== undefined) {
      obj = candidate;
    } else {
      break;
    }
  }
  return obj[props[i]];
}

var obj = {
  foo: {
    bar: {
      baz: 'x'
    }
  }
};

console.log(getPropByString(obj, 'foo.bar.baz')); // x
console.log(getPropByString(obj, 'foo.bar.baz.buk')); // undefined

If the access string is empty, returns the object. Otherwise, keeps going along access path until second last accessor. If that's an ojbect, returns the last object[accessor] value. Otherwise, returns undefined.

edited Sep 29 '21 at 21:35

answered Aug 02 '11 at 03:12

RobG

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Is there a way to get 'foo.bar.baz' dynamically? Like when you use Dev tools's console and navigate to a property, right click > copy path, but dynamically from the variable itself in this case (programmatically at runtime). Sounds weird, but I need that. I'm using angular and an UI framework called Syncfusion. Thanks. – Davi Daniel Siepmann Mar 11 '22 at 01:54
Just found my answer, using Object.getOwnPropertyDescriptors(obj) or Object.keys(obj) I have access to an object's prop names, than I have access/control over the whole object, without the need to give the path as a string. Just wondering if after minification it'll work, probably yes – Davi Daniel Siepmann Mar 11 '22 at 02:41
how about to get key just for v-model ? btw your code its work like a charm thanks you :D – Yogi Arif Widodo Sep 22 '22 at 22:23

score 36 · Answer 2 · edited Mar 09 '20 at 11:52

36

Using ES6:

var arr = { foo : 1, bar: { baz : 2 }, bee : 3 };
var {foo, bar, bar: {baz}, bee} = arr;

Same as:

// var foo = 1;
// var bar = {baz: 2};
// var baz = 2;
// var bee = 3;

Using lodash: https://lodash.com/docs#get

_.get(arr, 'bar.baz'); //returns 2;
_.get(arr, 'bar.baz[5].bazzz'); //returns undefined wont throw error;
_.get(arr, 'bar.baz[5].bazzz', 'defaultvalue'); // Returns defaultValue because result is undefined

edited Mar 09 '20 at 11:52

Nick is tired

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answered Nov 24 '15 at 16:48

Ninja

2,050
1
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27

1

Thank you, that's exactly what I was looking for. Its `_.set` friend is really useful too. – Michaël Perrin Jun 03 '16 at 12:41
Thank you for this! Lodash is certainly a pretty powerful lib – Sharky Feb 19 '22 at 13:55

score 16 · Answer 3 · answered Jul 07 '19 at 18:03

A recursive way :

   function getValue(obj, path) {
        if (!path) return obj;
        const properties = path.split('.');
        return getValue(obj[properties.shift()], properties.join('.'))
    }

    const myObj = {
        foo: {
            bar: {
                value: 'good'
            }
        }
    }

    console.log(getValue(myObj, 'foo.bar.value')); // good

score 13 · Accepted Answer · answered Aug 02 '11 at 00:52

How about change the getter function signature as getter('bar', 'baz') instead

function getter() {
  var v = arr;
  for(var i=0; i< arguments.length; i++) {
    if(!v) return null;
    v = v[arguments[i]];
  }
  return v;
}

ps. didn't test, but you get the idea ;)

score 8 · Answer 5 · answered Jan 24 '22 at 14:14

Using reduce we can fetch the value in single line of code.

const testobj = {b:{c:'1', d:{e:'2',f:'3'}}, g:{h:'3'}}

function fetchByDotOperator(object, value) {
    return value.split('.').reduce((acc, curr) => acc[curr], object);
}
console.log(fetchByDotOperator(testobj,'b.d.e'))

score 5 · Answer 6 · answered May 09 '19 at 21:08

A one liner for you:

const mock = {
  target: {
    "prop1": {
      "prop2": {
        "prop3": "sad"
      }
    }
  },
  path: "prop1.prop2.prop3",
  newValue: "happy"
};

mock.path.split(".").reduce(
  (acc, curr, i, src) =>
    (curr === src[src.length - 1]) ? acc[src[src.length - 1]] = mock.newValue : acc[curr], mock.target);


console.log(mock.target); //? { prop1: { prop2: { prop3: 'happy' } } }

score 5 · Answer 7 · answered Sep 27 '22 at 19:04

5

Here's a very simple one liner which grants you dynamic access via "foo.bar.baz" mechanism,

var obj = {
  foo: {
    bar: {
      baz: 'foobarbaz'
    }
  }
}
const nestedAccess = "foo.bar.baz";
console.log(nestedAccess.split('.').reduce((prev, cur) => prev[cur], obj)) //'foobarbaz'

answered Sep 27 '22 at 19:04

Abdullah Sohail

355
4
8

Is there a simple way to deal with arrays? Like `"foo.bar[2].baz"` for example? – leleogere Feb 14 '23 at 17:02

Redu · Answer 8 · 2016-05-06T12:16:25.883

I have recently developed my own Object method to get an object property nested among objects and arrays regardless how deep it is. It utilizes a single line of recursive approach. Check this out.

Object.prototype.getNestedValue = function(...a) {
  return a.length > 1 ? (this[a[0]] !== void 0 && this[a[0]].getNestedValue(...a.slice(1))) : this[a[0]];
};

var myObj = { foo : 1, bar: { baz : 2 }, bee : 3 },
   bazval = myObj.getNestedValue("bar","baz");

document.write(bazval);

Now let's check a deeper nested array object combo data structure

Object.prototype.getNestedValue = function(...a) {
  return a.length > 1 ? (this[a[0]] !== void 0 && this[a[0]].getNestedValue(...a.slice(1))) : this[a[0]];
};

var myArr = [{fox: [{turn:[857, 432]}]}, {sax: [{pana:[777, 987]}]}, {ton: [{joni:[123, 567]}]}, {piu: [{burn:[666, 37]}]}, {sia: [{foxy:[404, 696]}]}];
  
document.write(myArr.getNestedValue(3,"piu",0,"burn",1));

I believe being able to pass search parameters dynamically to existing array methods would make actions like searching, filtering or replacing of deeply nested structures much easy.

score 1 · Answer 9 · answered Nov 24 '20 at 13:53

1

 function getPropertyByString(object, propString) {
  let value = object;

  const props = propString.split('.');
  for (let index = 0; index < props.length; index += 1) {
    if (props[index] === undefined) break;
    value = value[props[index]];
  }
  return value;
};

const object = {
  name: 'any_name',
  address: {
    number: 77,
    test: {
      name: 'test'
    }
  }
}

console.log(getPropertyByString(object, 'address.test.name'))
// test

answered Nov 24 '20 at 13:53

Everton Miranda De Oliveira

183
1
4

Make sure to explain your answer so others can learn from it. – AlexH Nov 24 '20 at 14:21
@AlexH I tried to make the code self-explanatory, but I appreciate the suggestion. – Everton Miranda De Oliveira Nov 24 '20 at 14:56

score 1 · Answer 10 · edited Sep 22 '21 at 08:36

Above answers help you access nested objects only, however you might also want to access data in an object/array data type. You can try this recusive method:

const getValue = (obj, key) => {
  const keyParts = key.split(".");
  return getValueHelper(obj, keyParts);
};

const getValueHelper = (obj, keyParts) => {
  if (keyParts.length == 0) return obj;
  let key = keyParts.shift();
  if (Array.isArray(obj[key])) {
    return obj[key].map((x) => getValueHelper(x, [...keyParts])).flat();
  }
  return getValueHelper(obj[key], [...keyParts]);
};


//Examples

let data1 = {
  a: [{ b: { c: [{ d: [{ e: 1 }] }] } }, { b: { c: [{ d: [{ e: 2 }] }] } }],
};

console.log(getValue(data1, "a.b.c.d.e"));

//Output
//[ 1, 2 ]

let data2 = {
  a:{b:1},
};

console.log(getValue(data2, "a.b"));
//Output
//1

p.s. Remove .flat() to get desired output for arrays.

score 1 · Answer 11 · answered Aug 02 '11 at 00:52

You can access the functions arguments where you can pass any number of strings. I also recommend using arr as a parameter for better encapsulation:

function getter() {
    var current = arguments[0];
    for(var i = 1; i < arguments.length; i++) {
        if(current[arguments[i]]) {
            current = current[arguments[i]];
        } else {
            return null;
        }
    }
    return current;
}

var arr = { foo : 1, bar: { baz : 2 }, bee : 3 };
var baz = getter(arr, 'bar', 'baz');

score 0 · Answer 12 · answered Apr 12 '13 at 14:44

Theres a function defined on this blog to safely read nested properties from a JS object

It allows you to mine an object for properties... ie.

safeRead(arr, 'foo', 'bar', 'baz');

and if any part of the object chain is null or undefined it returns an empty string....

Abhijeet Bagul · Answer 13 · 2021-10-28T12:35:37.887

0

let obj = {foo : {bar: {baz:1}}}; // -- simply

console.log(eval('obj.foo.bar.baz')); //-- 1

// -- safer

val = "";
try {
    val = eval('Obj.foo.bar.baz')
}
catch(e) {
    val = "empty"
}

// -- val = 1

// -- use at your risk ;)

edited Oct 28 '21 at 12:35

answered Oct 28 '21 at 12:07

Abhijeet Bagul

19
2

there are certain situations where this is the most elegant solution, eval haters be damned. might run into trouble with scope in the eval when using more complex/dynamically concatenated chain strings though. – keymap Apr 29 '22 at 03:56

Matheus Felipe · Answer 14 · 2022-02-17T01:33:52.627

Here I created a small suite of functions to 'get / 'set' / 'push' / 'pull' from object nested properties.

inputObject : Target object. Ex: obj = {a:1, b:{c:2,d:3}}

propertyString : String containing the key to access. Ex: "b.c"

Finally:

_getObjectValueByPathString(obj, "b.c") would return 2

function _getObjectValueByPathString(inputObject, propertyString) {
    let splitStr = propertyString.split('.');

    if (!inputObject.hasOwnProperty(splitStr[0])) return undefined;

    if (splitStr.length === 1) {
        return inputObject[splitStr[0]];
    }
    else if (splitStr.length > 1) {
        let newPropertyString = "";
        let firstValue = splitStr.shift();

        splitStr.forEach((subStr, i) => {
            newPropertyString = i === 0 ? subStr : newPropertyString.concat(`.${subStr}`);
        });

        return _getObjectValueByPathString(inputObject[firstValue], newPropertyString);
    }
    else {
        throw "Invalid property string provided";
    }
}

function _setObjectValueByPathString(inputObject, propertyString, inputValue) {
    let splitStr = propertyString.split('.');

    if (splitStr.length === 1) {
        inputObject[splitStr[0]] = inputValue;
        return;
    }
    else if (splitStr.length > 1) {
        let newPropertyString = "";
        let firstValue = splitStr.shift();

        splitStr.forEach((subStr, i) => {
            newPropertyString = i === 0 ? subStr : newPropertyString.concat(`.${subStr}`);
        });

        _setObjectValueByPathString(inputObject[firstValue], newPropertyString, inputValue);
        return;
    }
    else {
        throw "Invalid property string provided";
    }
}

function _pushObjectValueByPathString(inputObject, propertyString, inputValue) {
    let splitStr = propertyString.split('.');

    if (splitStr.length === 1) {
        inputObject[splitStr[0]].push(inputValue);
        return;
    }
    else if (splitStr.length > 1) {
        let newPropertyString = "";
        let firstValue = splitStr.shift();

        splitStr.forEach((subStr, i) => {
            newPropertyString = i === 0 ? subStr : newPropertyString.concat(`.${subStr}`);
        });

        _pushObjectValueByPathString(inputObject[firstValue], newPropertyString, inputValue);
        return;
    }
    else {
        throw "Invalid property string provided";
    }
}

function _pullObjectValueByPathString(inputObject, propertyString, inputValue) {
    let splitStr = propertyString.split('.');

    if (splitStr.length === 1) {
        inputObject[splitStr[0]].pull(inputValue);
        return;
    }
    else if (splitStr.length > 1) {
        let newPropertyString = "";
        let firstValue = splitStr.shift();

        splitStr.forEach((subStr, i) => {
            newPropertyString = i === 0 ? subStr : newPropertyString.concat(`.${subStr}`);
        });

        _pullObjectValueByPathString(inputObject[firstValue], newPropertyString, inputValue);
        return;
    }
    else {
        throw "Invalid property string provided";
    }
}

In javascript how can I dynamically get a nested property of an object

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