How to loop through a plain JavaScript object with the objects as members?

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"
    }
}

Answers:

Answer
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]);
    }
}
Answer

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]);

});

Answer

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]);
         }
      }
   }
}
Answer

In ES6/2015 you can loop through an object like this: (using 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.
});

jsbin

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));

jsbin

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.
  });
};

jsbin

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.
    })
  );
Answer

Using Underscore.js’s _.each:

_.each(validation_messages, function(value, key){
    _.each(value, function(value, key){
        console.log(value);
    });
});
Answer

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
}

*/
Answer

This answer is an aggregate of the solutions that were provided in this post with some performance feedbacks. I think there is 2 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 cautious, 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 app 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 values,

? the of and Object.values approach

let v;
for (v of Object.values(obj)) {

}

More feedbacks about the tests :

  • Caching Object.keys or Object.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 native for loop with cached variables in Firefox seems to be a little faster than using a for...of loop. However the difference is not that important and Chrome is running for...of faster than native for loop, so I would recommend to use for...of when dealing with Object.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 use Object.keys. Plus Chrome is running both structure at equal speed (1st and last tests).

You can check the tests here : https://jsperf.com/es7-and-misc-loops

Answer

I know it's waaay late, but it did take me 2 minutes to write this 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]);
            }

        }

    }

}
Answer
for(var k in validation_messages) {
    var o = validation_messages[k];
    do_something_with(o.your_name);
    do_something_else_with(o.your_msg);
}
Answer

p is the value

for (var key in p) {
  alert(key + ' => ' + p[key]);
}

OR

Object.keys(p).forEach(key => { console.log(key, p[key]) })
Answer

In ES7 you can do:

for (const [key, value] of Object.entries(obj)) {
  //
}
Answer
for(var key in validation_messages){
    for(var subkey in validation_messages[key]){
        //code here
        //subkey being value, key being 'yourname' / 'yourmsg'
    }
}
Answer

Few ways to do that...

1) 2 layers 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);
Answer

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.

Answer

Another option:

var testObj = {test: true, test1: false};
for(let x of Object.keys(testObj)){
    console.log(x);
}
Answer

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
Answer

I think it's worth pointing out that jQuery sorts this out nicely with $.each().

See: https://api.jquery.com/each/

For 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.

Answer

var obj={
name:"SanD",
age:"27"
}
Object.keys(obj).forEach((key)=>console.log(key,obj[key]));

To loop through JavaScript Object we can use forEach and to optimize code we can use arrow function

Answer

I couldn't get the above posts 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
Answer

The solution that work 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;
}
Answer

In my case (on the basis of the preceding) is possible 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"]
Answer

Exotic one - for 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 whole object and nested objects - on each level you will get all fields and values. If you need to get 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;
})

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