Javascript: how to dynamically create nested objects using object names given by an array

I hope someone can help me with this Javascript.

I have an Object called "Settings" and I would like to write a function that adds new settings to that object.

The new setting's name and value are provided as strings. The string giving the setting's name is then split by the underscores into an array. The new setting should get added to the existing "Settings" object by creating new nested objects with the names given by each part of the array, except the last part which should be a string giving the setting's value. I should then be able to refer to the setting and e.g. alert its value. I can do this in a static way like this...

var Settings = {};
var newSettingName = "Modules_Video_Plugin";
var newSettingValue = "JWPlayer";
var newSettingNameArray = newSettingName.split("_");

Settings[newSettingNameArray[0]] = {};
Settings[newSettingNameArray[0]][newSettingNameArray[1]] = {};
Settings[newSettingNameArray[0]][newSettingNameArray[1]][newSettingNameArray[2]] = newSettingValue;

alert(Settings.Modules.Mediaplayers.Video.Plugin);

... the part that creates the nested objects is doing this ...

Settings["Modules"] = {};
Settings["Modules"]["Video"] = {};
Settings["Modules"]["Video"]["Plugin"] = "JWPlayer";

However, as the number of parts that make up the setting name can vary, e.g. a newSettingName could be "Modules_Floorplan_Image_Src", I'd like to do this dynamically using a function such as...

createSetting (newSettingNameArray, newSettingValue);

function createSetting(setting, value) {
	// code to create new setting goes here
}

Can anyone help me work out how to do this dynamically?

I presume there has to be a for...loop in there to itterate through the array, but I haven't been able to work out a way to create the nested objects.

If you've got this far thanks very much for taking the time to read even if you can't help.

Put in a function, short and fast (no recursion).

var createNestedObject = function( base, names ) {
	for( var i = 0; i < names.length; i++ ) {
		base = base[ names[i] ] = base[ names[i] ] || {};
	}
};

// Usage:
createNestedObject( window, ["shapes", "triangle", "points"] );
// Now window.shapes.triangle.points is an empty object, ready to be used.

It skips already existing parts of the hierarchy. Useful if you are not sure whether the hierarchy was already created.

Or:

A fancier version where you can directly assign the value to the last object in the hierarchy, and you can chain function calls because it returns the last object.

// Function: createNestedObject( base, names[, value] )
//   base: the object on which to create the hierarchy
//   names: an array of strings contaning the names of the objects
//   value (optional): if given, will be the last object in the hierarchy
// Returns: the last object in the hierarchy
var createNestedObject = function( base, names, value ) {
	// If a value is given, remove the last name and keep it for later:
	var lastName = arguments.length === 3 ? names.pop() : false;
	
	// Walk the hierarchy, creating new objects where needed.
	// If the lastName was removed, then the last object is not set yet:
	for( var i = 0; i < names.length; i++ ) {
		base = base[ names[i] ] = base[ names[i] ] || {};
	}
	
	// If a value was given, set it to the last name:
	if( lastName ) base = base[ lastName ] = value;
	
	// Return the last object in the hierarchy:
	return base;
};

// Usages:

createNestedObject( window, ["shapes", "circle"] );
// Now window.shapes.circle is an empty object, ready to be used.

var obj = {}; // Works with any object other that window too
createNestedObject( obj, ["shapes", "rectangle", "width"], 300 );
// Now we have: obj.shapes.rectangle.width === 300

createNestedObject( obj, "shapes.rectangle.height".split('.'), 400 );
// Now we have: obj.shapes.rectangle.height === 400

Note: if your hierarchy needs to be built from values other that standard objects (ie. not {}), see also TimDog's answer below.

Edit: uses regular loops instead of for...in loops. It's safer in cases where a library modifies the Array prototype.

function assign(obj, keyPath, value) {
   lastKeyIndex = keyPath.length-1;
   for (var i = 0; i < lastKeyIndex; ++ i) {
     key = keyPath[i];
     if (!(key in obj)){
       obj[key] = {}
     }
     obj = obj[key];
   }
   obj[keyPath[lastKeyIndex]] = value;
}

Usage:

var settings = {};
assign(settings, ['Modules', 'Video', 'Plugin'], 'JWPlayer');

My ES2015 solution. Keeps existing values.

const set = (obj, path, val) => { 
    const keys = path.split('.');
    const lastKey = keys.pop();
    const lastObj = keys.reduce((obj, key) => 
        obj[key] = obj[key] || {}, 
        obj); 
    lastObj[lastKey] = val;
};

Example:

const obj = {'a': {'prop': {'that': 'exists'}}};
set(obj, 'a.very.deep.prop', 'value');
console.log(JSON.stringify(obj));
// {"a":{"prop":{"that":"exists"},"very":{"deep":{"prop":"value"}}}}

Using ES6 is shorten. Set your path into an array. first, you have to reverse the array, to start filling the object.

let obj = ['a','b','c'] // {a:{b:{c:{}}}
obj.reverse();

const nestedObject = obj.reduce((prev, current) => (
    {[current]:{...prev}}
), {});

Another recursive solution:

var nest = function(obj, keys, v) {
    if (keys.length === 1) {
      obj[keys[0]] = v;
    } else {
      var key = keys.shift();
      obj[key] = nest(typeof obj[key] === 'undefined' ? {} : obj[key], keys, v);
    }

    return obj;
};

Example usage:

var dog = {bark: {sound: 'bark!'}};
nest(dog, ['bark', 'loudness'], 66);
nest(dog, ['woff', 'sound'], 'woff!');
console.log(dog); // {bark: {loudness: 66, sound: "bark!"}, woff: {sound: "woff!"}}

I love this ES6 immutable way to set certain value on nested field:

const setValueToField = (fields, value) => {
  const reducer = (acc, item, index, arr) => ({ [item]: index + 1 < arr.length ? acc : value });
  return fields.reduceRight(reducer, {});
};

And then use it with creating your target object.

const targetObject = setValueToField(['one', 'two', 'three'], 'nice');
console.log(targetObject); // Output: { one: { two: { three: 'nice' } } }

Here is a simple tweak to jlgrall's answer that allows setting distinct values on each element in the nested hierarchy:

var createNestedObject = function( base, names, values ) {
    for( var i in names ) base = base[ names[i] ] = base[ names[i] ] || (values[i] || {});
};

Hope it helps.

Lodash has a _.set method to achieve this

let obj = {}

_.set(obj, ['a', 'b', 'c', 'd'], 'e')

or

_.set(obj, 'a.b.c.d', 'e')

// which generate the following object
{
   "a": {
      "b": {
         "c": {
            "d": "e"
         }
      }
   }
}

Here is a functional solution to dynamically create nested objects.

const nest = (path, obj) => {
  const reversedPath = path.split('.').reverse();
  
  const iter = ([head, ...tail], obj) => {
  	if (!head) {
      return obj;
    }
    const newObj = {[head]: {...obj}};
    return iter(tail, newObj);
  }
  return iter(reversedPath, obj);
}

Example:

const data = {prop: 'someData'};
const path = 'a.deep.path';
const result = nest(path, data);
console.log(JSON.stringify(result));
// {"a":{"deep":{"path":{"prop":"someData"}}}}

Inspired by ImmutableJS setIn method which will never mutate the original. This works with mixed array and object nested values.

function setIn(obj = {}, [prop, ...rest], value) {
    const newObj = Array.isArray(obj) ? [...obj] : {...obj};
    newObj[prop] = rest.length ? setIn(obj[prop], rest, value) : value;
    return newObj;
}

var obj = {
  a: {
    b: {
      c: [
        {d: 5}
      ]
    }
  }
};

const newObj = setIn(obj, ["a", "b", "c", 0, "x"], "new");

//obj === {a: {b: {c: [{d: 5}]}}}
//newObj === {a: {b: {c: [{d: 5, x: "new"}]}}}

Appreciate that this question is mega old! But after coming across a need to do something like this in node, I made a module and published it to npm. Nestob

var nestob = require('nestob');

//Create a new nestable object - instead of the standard js object ({})
var newNested = new nestob.Nestable();

//Set nested object properties without having to create the objects first!
newNested.setNested('biscuits.oblong.marmaduke', 'cheese');
newNested.setNested(['orange', 'tartan', 'pipedream'], { poppers: 'astray', numbers: [123,456,789]});

console.log(newNested, newNested.orange.tartan.pipedream);
//{ biscuits: { oblong: { marmaduke: 'cheese' } },
  orange: { tartan: { pipedream: [Object] } } } { poppers: 'astray', numbers: [ 123, 456, 789 ] }

//Get nested object properties without having to worry about whether the objects exist
//Pass in a default value to be returned if desired
console.log(newNested.getNested('generic.yoghurt.asguard', 'autodrome'));
//autodrome

//You can also pass in an array containing the object keys
console.log(newNested.getNested(['chosp', 'umbridge', 'dollar'], 'symbols'));
//symbols

//You can also use nestob to modify objects not created using nestob
var normalObj = {};

nestob.setNested(normalObj, 'running.out.of', 'words');

console.log(normalObj);
//{ running: { out: { of: 'words' } } }

console.log(nestob.getNested(normalObj, 'random.things', 'indigo'));
//indigo
console.log(nestob.getNested(normalObj, 'improbable.apricots'));
//false

Inside your loop you can use lodash.set and will create the path for you:

...
const set = require('lodash.set');

const p = {};
const [type, lang, name] = f.split('.');
set(p, [lang, type, name], '');

console.log(p);
// { lang: { 'type': { 'name': '' }}}

try using recursive function:

function createSetting(setting, value, index) {
  if (typeof index !== 'number') {
    index = 0;
  }
  
  if (index+1 == setting.length ) {
    settings[setting[index]] = value;
  }
  else {
    settings[setting[index]] = {};
    createSetting(setting, value, ++index);
  }
}

I think, this is shorter:

Settings = {};
newSettingName = "Modules_Floorplan_Image_Src";
newSettingValue = "JWPlayer";
newSettingNameArray = newSettingName.split("_");

a = Settings;
for (var i = 0 in newSettingNameArray) {
    var x = newSettingNameArray[i];
    a[x] = i == newSettingNameArray.length-1 ? newSettingValue : {};
    a = a[x];
}

I found @jlgrall's answer was great but after simplifying it, it didn't work in Chrome. Here's my fixed should anyone want a lite version:

var callback = 'fn.item1.item2.callbackfunction',
    cb = callback.split('.'),
    baseObj = window;

function createNestedObject(base, items){
    $.each(items, function(i, v){
        base = base[v] = (base[v] || {});
    });
}

callbackFunction = createNestedObject(baseObj, cb);

console.log(callbackFunction);

I hope this is useful and relevant. Sorry, I've just smashed this example out...

You can define your own Object methods; also I'm using underscore for brevity:

var _ = require('underscore');

// a fast get method for object, by specifying an address with depth
Object.prototype.pick = function(addr) {
    if (!_.isArray(addr)) return this[addr]; // if isn't array, just get normally
    var tmpo = this;
    while (i = addr.shift())
        tmpo = tmpo[i];
    return tmpo;
};
// a fast set method for object, put value at obj[addr]
Object.prototype.put = function(addr, val) {
    if (!_.isArray(addr)) this[addr] = val; // if isn't array, just set normally
    this.pick(_.initial(addr))[_.last(addr)] = val;
};

Sample usage:

var obj = { 
           'foo': {
                   'bar': 0 }}

obj.pick('foo'); // returns { bar: 0 }
obj.pick(['foo','bar']); // returns 0
obj.put(['foo', 'bar'], -1) // obj becomes {'foo': {'bar': -1}}

A snippet for those who need to create a nested objects with support of array keys to set a value to the end of path. Path is the string like: modal.product.action.review.2.write.survey.data. Based on jlgrall version.

var updateStateQuery = function(state, path, value) {
	var names = path.split('.');
	for (var i = 0, len = names.length; i < len; i++) {
		if (i == (len - 1)) {
			state = state[names[i]] = state[names[i]] || value;
		}
		else if (parseInt(names[i+1]) >= 0) {
			state = state[names[i]] = state[names[i]] || [];
		}
		else {
			state = state[names[i]] = state[names[i]] || {};
		}
	}
};

Set Nested Data:

function setNestedData(root, path, value) {
  var paths = path.split('.');
  var last_index = paths.length - 1;
  paths.forEach(function(key, index) {
    if (!(key in root)) root[key] = {};
    if (index==last_index) root[key] = value;
    root = root[key];
  });
  return root;
}

var obj = {'existing': 'value'};
setNestedData(obj, 'animal.fish.pet', 'derp');
setNestedData(obj, 'animal.cat.pet', 'musubi');
console.log(JSON.stringify(obj));
// {"existing":"value","animal":{"fish":{"pet":"derp"},"cat":{"pet":"musubi"}}}

Get Nested Data:

function getNestedData(obj, path) {
  var index = function(obj, i) { return obj && obj[i]; };
  return path.split('.').reduce(index, obj);
}
getNestedData(obj, 'animal.cat.pet')
// "musubi"
getNestedData(obj, 'animal.dog.pet')
// undefined

Eval is probably overkill but the result is simple to visualize, with no nested loops or recursion.

 function buildDir(obj, path){
   var paths = path.split('_');
   var final = paths.pop();
   for (let i = 1; i <= paths.length; i++) {
     var key = "obj['" + paths.slice(0, i).join("']['") + "']"
     console.log(key)
     eval(`${key} = {}`)
   }
   eval(`${key} = '${final}'`)
   return obj
 }

 var newSettingName = "Modules_Video_Plugin_JWPlayer";
 var Settings = buildDir( {}, newSettingName );

Basically you are progressively writing a string "obj['one']= {}", "obj['one']['two']"= {} and evaling it;

Try this: https://github.com/silkyland/object-to-formdata

var obj2fd = require('obj2fd/es5').default
var fd = obj2fd({
             a:1,
             b:[
                {c: 3},
                {d: 4}
             ]
})

Result :

fd = [
       a => 1,
       b => [
         c => 3,
         d => 4
       ]
]

Here is a decomposition to several useful functions, that each preserve existing data. Does not handle arrays.

• setDeep: Answers question. Non-destructive to other data in the object.
• setDefaultDeep: Same, but only sets if not already set.
• setDefault: Sets a key if not already set. Same as Python's setdefault.
• setStructure: Helper function that builds the path.

// Create a nested structure of objects along path within obj. Only overwrites the final value.
let setDeep = (obj, path, value) =>
    setStructure(obj, path.slice(0, -1))[path[path.length - 1]] = value

// Create a nested structure of objects along path within obj. Does not overwrite any value.
let setDefaultDeep = (obj, path, value) =>
    setDefault(setStructure(obj, path.slice(0, -1)), path[path.length - 1], value)

// Set obj[key] to value if key is not in object, and return obj[key]
let setDefault = (obj, key, value) =>
    obj[key] = key in obj ? obj[key] : value;

// Create a nested structure of objects along path within obj. Does not overwrite any value.
let setStructure = (obj, path) => 
    path.reduce((obj, segment) => setDefault(obj, segment, {}), obj);



// EXAMPLES
let temp = {};

// returns the set value, similar to assignment
console.log('temp.a.b.c.d:', 
            setDeep(temp, ['a', 'b', 'c', 'd'], 'one'))

// not destructive to 'one'
setDeep(temp, ['a', 'b', 'z'], 'two')

// does not overwrite, returns previously set value
console.log('temp.a.b.z:  ', 
            setDefaultDeep(temp, ['a', 'b', 'z'], 'unused'))

// creates new, returns current value
console.log('temp["a.1"]: ', 
            setDefault(temp, 'a.1', 'three'))

// can also be used as a getter
console.log("temp.x.y.z:  ", 
            setStructure(temp, ['x', 'y', 'z']))


console.log("final object:", temp)

I'm not sure why anyone would want string paths:

1. They are ambiguous for keys with periods
2. You have to build the strings in the first place

Since I started with something from this page, I wanted to contribute back

Other examples overwrote the final node even if it was set, and that wasn't what I wanted.

Also, if returnObj is set to true, it returns the base object. By default, falsy, it returns the deepest node.

function param(obj, path, value, returnObj) {
  if (typeof path == 'string') path = path.split(".");
  var child = obj;
  path.forEach((key, i) => {
    if (!(key in child)) {
      child[key] = (i < path.length-1) ? {} : value || {};
    }
    child = child[key];
  });
  return returnObj ? obj : child;
}

var x = {};
var xOut = param(x, "y.z", "setting")
console.log(xOut);
xOut = param(x, "y.z", "overwrite") // won't set
console.log(xOut);
xOut = param(x, "y.a", "setting2")
console.log(xOut);
xOut = param(x, "y.a", "setting2", true) // get object rather than deepest node.
console.log(xOut);

You can also do something where numeric keys are placed in arrays (if they don't already exist). Note that numeric keys won't convert to arrays for the first element of the path, since that's set by the type of your base-object.

function isNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

function param(obj, path, value, returnObj) {
  if (typeof path == 'string') path = path.split(".");
  var child = obj;
  path.forEach((key, i) => {
    var nextKey = path[i+1];
    if (!(key in child)) {
      child[key] = (nextKey == undefined && value != undefined 
        ? value 
        : isNumber(nextKey)
          ? []
          : {});
    }
    child = child[key];
  });
  return returnObj ? obj : child;
}

var x = {};

var xOut = param(x, "y.z", "setting")
console.log(xOut);
xOut = param(x, "y.z", "overwrite") // won't set
console.log(xOut);
xOut = param(x, "y.a", "setting2")
console.log(xOut);
xOut = param(x, "y.a", "setting2", true) // get object rather than deepest node.
xOut = param(x, "1.0.2.a", "setting")
xOut = param(x, "1.0.1.a", "try to override") // won't set
xOut = param(x, "1.0.5.a", "new-setting", true) // get object rather than deepest node.
console.log(xOut);

Naturally, when the numeric keys are greater than 0, you might see some undefined gaps.

Practical uses of this might be

function AddNote(book, page, line) {
  // assume a global global notes collection
  var myNotes = param(allNotes, [book, page, line], []);
  myNotes.push('This was a great twist!')
  return myNotes;
}

var allNotes = {}
var youthfulHopes = AddNote('A Game of Thrones', 4, 2, "I'm already hooked, at least I won't have to wait long for the books to come out!");

console.log(allNotes)
// {"A Game of Thrones": [undefined, undefined, undefined, undefined, [undefined, undefined, ["I'm already hooked, at least I won't have to wait long for the books to come out!"]]]}
console.log(youthfulHopes)
// ["I'm already hooked, at least I won't have to wait long for the books to come out!"]

function initPath(obj, path) {
  path.split('.').reduce((o, key) => (
    Object.assign(o, {[key]: Object(o[key])}),
    o[key]
  ), obj);
  return obj;
}

Usage

const obj = { a: { b: 'value1' } };
initPath(obj, 'a.c.d').a.c.d='value2';
/*
{
  "a": {
    "b": "value1",
    "c": {
      "d": "value2"
    }
  }
}
*/

simple answer. on es6, im using this

const assign = (obj, path, value) => {
  let keyPath = path.split('.')
  let lastKeyIndex = keyPath.length - 1
  for (let i = 0; i < lastKeyIndex; ++i) {
    let key = keyPath[i]
    if (!(key in obj)) {
      obj[key] = {}
    }
    obj = obj[key]
  }
  obj[keyPath[lastKeyIndex]] = value
}

example json

const obj = {
  b: 'hello'
}

you can add new key

assign(obj, 'c.d.e', 'this value')

and you get like bellow

console.log(obj)
//response example
obj = {
   b: 'hello',
   c: {
      d: {
         e: 'this value'
      }
   }
}

function createObj(keys, value) {
	let obj = {}
  let schema = obj
	keys = keys.split('.')
  
  for (let i = 0; i < keys.length - 1; i++) {
  	schema[keys[i]] = {}
    schema = schema[keys[i]]
  }
  
  schema[keys.pop()] = value

	return obj
}


let keys = 'value1.value2.value3'
let value = 'Hello'

let obj = createObj(keys, value)