How to loop through a plain JavaScript object with the objects as members
JavascriptLoopsJavascript Problem Overview
How can I loop through all members in a JavaScript object, including values that are objects?
For example, how could I loop through this (accessing the "your_name" and "your_message" for each)?
var validation_messages = {
"key_1": {
"your_name": "jimmy",
"your_msg": "hello world"
},
"key_2": {
"your_name": "billy",
"your_msg": "foo equals bar"
}
}
Javascript Solutions
Solution 1 - Javascript
for (var key in validation_messages) {
// skip loop if the property is from prototype
if (!validation_messages.hasOwnProperty(key)) continue;
var obj = validation_messages[key];
for (var prop in obj) {
// skip loop if the property is from prototype
if (!obj.hasOwnProperty(prop)) continue;
// your code
alert(prop + " = " + obj[prop]);
}
}
Solution 2 - Javascript
Under ECMAScript 5, you can combine Object.keys()
and Array.prototype.forEach()
:
var obj = {
first: "John",
last: "Doe"
};
//
// Visit non-inherited enumerable keys
//
Object.keys(obj).forEach(function(key) {
console.log(key, obj[key]);
});
Solution 3 - Javascript
In ES6/2015 you can loop through an object like this (using the arrow function):
Object.keys(myObj).forEach(key => {
console.log(key); // the name of the current key.
console.log(myObj[key]); // the value of the current key.
});
In ES7/2016 you can use Object.entries
instead of Object.keys
and loop through an object like this:
Object.entries(myObj).forEach(([key, val]) => {
console.log(key); // the name of the current key.
console.log(val); // the value of the current key.
});
The above would also work as a one-liner:
Object.entries(myObj).forEach(([key, val]) => console.log(key, val));
In case you want to loop through nested objects as well, you can use a recursive function (ES6):
const loopNestedObj = obj => {
Object.keys(obj).forEach(key => {
if (obj[key] && typeof obj[key] === "object") loopNestedObj(obj[key]); // recurse.
else console.log(key, obj[key]); // or do something with key and val.
});
};
The same as function above, but with ES7 Object.entries()
instead of Object.keys()
:
const loopNestedObj = obj => {
Object.entries(obj).forEach(([key, val]) => {
if (val && typeof val === "object") loopNestedObj(val); // recurse.
else console.log(key, val); // or do something with key and val.
});
};
Here we loop through nested objects change values and return a new object in one go using Object.entries()
combined with Object.fromEntries()
(ES10/2019):
const loopNestedObj = obj =>
Object.fromEntries(
Object.entries(obj).map(([key, val]) => {
if (val && typeof val === "object") [key, loopNestedObj(val)]; // recurse
else [key, updateMyVal(val)]; // or do something with key and val.
})
);
Another way of looping through objects is by using for ... in and for ... of. See vdegenne's nicely written answer.
Solution 4 - Javascript
The problem with this
for (var key in validation_messages) {
var obj = validation_messages[key];
for (var prop in obj) {
alert(prop + " = " + obj[prop]);
}
}
is that you’ll also loop through the primitive object's prototype.
With this one you will avoid it:
for (var key in validation_messages) {
if (validation_messages.hasOwnProperty(key)) {
var obj = validation_messages[key];
for (var prop in obj) {
if (obj.hasOwnProperty(prop)) {
alert(prop + " = " + obj[prop]);
}
}
}
}
Solution 5 - Javascript
Using Underscore.js’s _.each
:
_.each(validation_messages, function(value, key){
_.each(value, function(value, key){
console.log(value);
});
});
Solution 6 - Javascript
If you use recursion you can return object properties of any depth-
function lookdeep(object){
var collection= [], index= 0, next, item;
for(item in object){
if(object.hasOwnProperty(item)){
next= object[item];
if(typeof next== 'object' && next!= null){
collection[index++]= item +
':{ '+ lookdeep(next).join(', ')+'}';
}
else collection[index++]= [item+':'+String(next)];
}
}
return collection;
}
//example
var O={
a:1, b:2, c:{
c1:3, c2:4, c3:{
t:true, f:false
}
},
d:11
};
var lookdeepSample= 'O={'+ lookdeep(O).join(',\n')+'}';
/* returned value: (String)
O={
a:1,
b:2,
c:{
c1:3, c2:4, c3:{
t:true, f:false
}
},
d:11
}
*/
Solution 7 - Javascript
> This answer is an aggregate of the solutions that were provided in this > post with some performance feedbacks. I think there is two > use cases and the OP didn't mention if he needs to access the keys in order use them > during the loop process.
I. The keys need to be accessed
✔ The of
and Object.keys
approach
let k;
for (k of Object.keys(obj)) {
/* k : key
* obj[k] : value
*/
}
✔ The in
approach
let k;
for (k in obj) {
/* k : key
* obj[k] : value
*/
}
Use this one with caution, as it could print prototype'd properties of obj
✔ The ES7 approach
for (const [key, value] of Object.entries(obj)) {
}
However, at the time of the edit I wouldn't recommend the ES7 method, because JavaScript initializes a lot of variables internally to build this procedure (see the feedbacks for proof). Unless you are not developing a huge application which deserves optimization, then it is OK, but if optimization is your priority, you should think about it.
II. We just need to access each value
✔ The of
and Object.values
approach
let v;
for (v of Object.values(obj)) {
}
More feedbacks about the tests:
- Caching
Object.keys
orObject.values
performance is negligible
For instance,
const keys = Object.keys(obj);
let i;
for (i of keys) {
//
}
// same as
for (i of Object.keys(obj)) {
//
}
-
For
Object.values
case, using a nativefor
loop with cached variables in Firefox seems to be a little faster than using afor...of
loop. However, the difference is not that important and Chrome is runningfor...of
faster than nativefor
loop, so I would recommend to usefor...of
when dealing withObject.values
in any cases (4th and 6th tests). -
In Firefox, the
for...in
loop is really slow, so when we want to cache the key during the iteration it is better to useObject.keys
. Plus Chrome is running both structure at equal speed (first and last tests).
You can check the tests here: https://jsperf.com/es7-and-misc-loops
Solution 8 - Javascript
for(var k in validation_messages) {
var o = validation_messages[k];
do_something_with(o.your_name);
do_something_else_with(o.your_msg);
}
Solution 9 - Javascript
An optimized and improved version of AgileJon's answer:
var key, obj, prop, owns = Object.prototype.hasOwnProperty;
for (key in validation_messages ) {
if (owns.call(validation_messages, key)) {
obj = validation_messages[key];
for (prop in obj ) {
// Using obj.hasOwnProperty might cause you headache if there is
// obj.hasOwnProperty = function(){return false;}
// but 'owns' will always work
if (owns.call(obj, prop)) {
console.log(prop, "=", obj[prop]);
}
}
}
}
Solution 10 - Javascript
p is the value
for (var key in p) {
alert(key + ' => ' + p[key]);
}
OR
Object.keys(p).forEach(key => { console.log(key, p[key]) })
Solution 11 - Javascript
In ES7 you can do:
for (const [key, value] of Object.entries(obj)) {
//
}
Solution 12 - Javascript
for(var key in validation_messages){
for(var subkey in validation_messages[key]){
//code here
//subkey being value, key being 'yourname' / 'yourmsg'
}
}
Solution 13 - Javascript
A few ways to do that...
1) A two-layer for...in loop...
for (let key in validation_messages) {
const vmKeys = validation_messages[key];
for (let vmKey in vmKeys) {
console.log(vmKey + vmKeys[vmKey]);
}
}
2) Using Object.key
Object.keys(validation_messages).forEach(key => {
const vmKeys = validation_messages[key];
Object.keys(vmKeys).forEach(key => {
console.log(vmKeys + vmKeys[key]);
});
});
3) Recursive function
const recursiveObj = obj => {
for(let key in obj){
if(!obj.hasOwnProperty(key)) continue;
if(typeof obj[key] !== 'object'){
console.log(key + obj[key]);
} else {
recursiveObj(obj[key]);
}
}
}
And call it like:
recursiveObj(validation_messages);
Solution 14 - Javascript
Another option:
var testObj = {test: true, test1: false};
for(let x of Object.keys(testObj)){
console.log(x);
}
Solution 15 - Javascript
Here comes the improved and recursive version of AgileJon's solution (demo):
function loopThrough(obj){
for(var key in obj){
// skip loop if the property is from prototype
if(!obj.hasOwnProperty(key)) continue;
if(typeof obj[key] !== 'object'){
//your code
console.log(key+" = "+obj[key]);
} else {
loopThrough(obj[key]);
}
}
}
loopThrough(validation_messages);
This solution works for all kinds of different depths.
Solution 16 - Javascript
ECMAScript 2017, just finalized a month ago, introduces Object.values(). So now you can do this:
let v;
for (v of Object.values(validation_messages))
console.log(v.your_name); // jimmy billy
Solution 17 - Javascript
var validation_messages = {
"key_1": {
"your_name": "jimmy",
"your_msg": "hello world"
},
"key_2": {
"your_name": "billy",
"your_msg": "foo equals bar"
}
}
for (var i in validation_messages) {
console.log("i = \"" + i + "\"");
console.log("validation_messages[\"" + i + "\"] = ");
console.log(validation_messages[i]);
console.log("\n");
for (var j in validation_messages[i]) {
console.log("j = \"" + j + "\"");
console.log("validation_messages[\"" + i + "\"][\"" + j + "\"] = \"" + validation_messages[i][j] + "\"");
console.log("\n");
}
console.log('\n');
}
Outputs:
i = "key_1"
validation_messages["key_1"] =
{
your_name:"jimmy",
your_msg:"hello world"
}
j = "your_name"
validation_messages["key_1"]["your_name"] = "jimmy"
j = "your_msg"
validation_messages["key_1"]["your_msg"] = "hello world"
i = "key_2"
validation_messages["key_2"] =
{
your_name:"billy",
your_msg:"foo equals bar"
}
j = "your_name"
validation_messages["key_2"]["your_name"] = "billy"
j = "your_msg"
validation_messages["key_2"]["your_msg"] = "foo equals bar"
Solution 18 - Javascript
I couldn't get the previous answere to do quite what I was after.
After playing around with the other replies here, I made this. It's hacky, but it works!
For this object:
var myObj = {
pageURL : "BLAH",
emailBox : {model:"emailAddress", selector:"#emailAddress"},
passwordBox: {model:"password" , selector:"#password"}
};
... this code:
// Get every value in the object into a separate array item ...
function buildArray(p_MainObj, p_Name) {
var variableList = [];
var thisVar = "";
var thisYes = false;
for (var key in p_MainObj) {
thisVar = p_Name + "." + key;
thisYes = false;
if (p_MainObj.hasOwnProperty(key)) {
var obj = p_MainObj[key];
for (var prop in obj) {
var myregex = /^[0-9]*$/;
if (myregex.exec(prop) != prop) {
thisYes = true;
variableList.push({item:thisVar + "." + prop,value:obj[prop]});
}
}
if ( ! thisYes )
variableList.push({item:thisVar,value:obj});
}
}
return variableList;
}
// Get the object items into a simple array ...
var objectItems = buildArray(myObj, "myObj");
// Now use them / test them etc... as you need to!
for (var x=0; x < objectItems.length; ++x) {
console.log(objectItems[x].item + " = " + objectItems[x].value);
}
... produces this in the console:
myObj.pageURL = BLAH
myObj.emailBox.model = emailAddress
myObj.emailBox.selector = #emailAddress
myObj.passwordBox.model = password
myObj.passwordBox.selector = #password
Solution 19 - Javascript
I think it's worth pointing out that jQuery sorts this out nicely with $.each()
.
See: .each()
Example:
$('.foo').each(function() {
console.log($(this));
});
$(this)
being the single item inside the object. Swap $('.foo')
to a variable if you don't want to use jQuery's selector engine.
Solution 20 - Javascript
var obj = {
name: "SanD",
age: "27"
}
Object.keys(obj).forEach((key) => console.log(key,obj[key]));
To loop through the JavaScript Object we can use forEach and to optimize the code we can use the arrow function.
Solution 21 - Javascript
using lodash _.forEach:
_.forEach({ 'a': 1, 'b': 2 }, function(value, key) {
console.log(key, value);
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>
Solution 22 - Javascript
forEach2
(Found here):
var lunch = {
sandwich: 'ham',
age: 48,
};
lunch.forEach2(function (item, key) {
console.log(key);
console.log(item);
});
Code:
if (!Object.prototype.forEach2) {
Object.defineProperty(Object.prototype, 'forEach2', {
value: function (callback, thisArg) {
if (this == null) {
throw new TypeError('Not an object');
}
thisArg = thisArg || window;
for (var key in this) {
if (this.hasOwnProperty(key)) {
callback.call(thisArg, this[key], key, this);
}
}
}
});
}
Solution 23 - Javascript
The solution that works for me is the following:
_private.convertParams = function(params){
var params = [];
Object.keys(values).forEach(function(key) {
params.push({"id":key, "option":"Igual", "value":params[key].id})
});
return params;
}
Solution 24 - Javascript
Exotic one - deep traverse
JSON.stringify(validation_messages,(field,value)=>{
if(!field) return value;
// ... your code
return value;
})
In this solution we use replacer which allows to deep traverse the whole object and nested objects - on each level you will get all fields and values. If you need to get the full path to each field, look here.
var validation_messages = {
"key_1": {
"your_name": "jimmy",
"your_msg": "hello world"
},
"key_2": {
"your_name": "billy",
"your_msg": "foo equals bar",
"deep": {
"color": "red",
"size": "10px"
}
}
}
JSON.stringify(validation_messages,(field,value)=>{
if(!field) return value;
console.log(`key: ${field.padEnd(11)} - value: ${value}`);
return value;
})
Solution 25 - Javascript
Using ES8 Object.entries() should be a more compact way to achieve this.
Object.entries(validation_messages).map(([key,object]) => {
alert(`Looping through key : ${key}`);
Object.entries(object).map(([token, value]) => {
alert(`${token} : ${value}`);
});
});
Solution 26 - Javascript
In 2020 you want immutable and universal functions
This walks through your multidimensional object composed of sub-objects, arrays and string and apply a custom function:
export const iterate = (object, func) => {
const entries = Object.entries(object).map(([key, value]) =>
Array.isArray(value)
? [key, value.map(e => iterate(e, func))]
: typeof value === 'object'
? [key, iterate(value, func)]
: [key, func(value)]
);
return Object.fromEntries(entries);
};
Usage:
const r = iterate(data, e=>'converted_'+e);
console.log(r);
Solution 27 - Javascript
In my case (on the basis of the preceding) it is possible for any number of levels.
var myObj = {
rrr: undefined,
pageURL : "BLAH",
emailBox : {model:"emailAddress", selector:"#emailAddress"},
passwordBox: {model:"password" , selector:"#password"},
proba: {odin:{dva:"rr",trr:"tyuuu"}, od:{ff:5,ppa:{ooo:{lll:'lll'}},tyt:'12345'}}
};
function lookdeep(obj,p_Name,gg){
var A=[], tem, wrem=[], dd=gg?wrem:A;
for(var p in obj){
var y1=gg?'':p_Name, y1=y1 + '.' + p;
if(obj.hasOwnProperty(p)){
var tem=obj[p];
if(tem && typeof tem=='object'){
a1=arguments.callee(tem,p_Name,true);
if(a1 && typeof a1=='object'){for(i in a1){dd.push(y1 + a1[i])};}
}
else{
dd.push(y1 + ':' + String(tem));
}
}
};
return dd
};
var s=lookdeep(myObj,'myObj',false);
for (var x=0; x < s.length; ++x) {
console.log(s[x]+'\n');}
Result:
["myObj.rrr:undefined","myObj.pageURL:BLAH","myObj.emailBox.model:emailAddress","myObj.emailBox.selector:#emailAddress","myObj.passwordBox.model:password","myObj.passwordBox.selector:#password","myObj.proba.odin.dva:rr","myObj.proba.odin.trr:tyuuu","myObj.proba.od.ff:5","myObj.proba.od.ppa.ooo.lll:lll","myObj.proba.od.tyt:12345"]