Getting the object's property name

Question

I was wondering if there was any way in JavaScript to loop through an object like so.

for(var i in myObject) {
    // ...
}

But get the name of each property like this.

for(var i in myObject) {
    separateObj[myObject[i].name] = myObject[i];
}

I can't seem to find anything like it on Google. They say to pass the names of the variables with them but this is not an option for what I am trying to achieve.

Thanks for any help you can offer.

Answer 1

Use Object.keys():

var myObject = { a: 'c', b: 'a', c: 'b' };
var keyNames = Object.keys(myObject);
console.log(keyNames); // Outputs ["a","b","c"]

Object.keys() gives you an array of property names belonging to the input object.

Answer 2

i is the name.

for(var name in obj) {
    alert(name);
    var value = obj[name];
    alert(value);
}

So you could do:

seperateObj[i] = myObject[i];

Answer 3

Disclaimer I misunderstood the question to be: "Can I know the property name that an object was attached to", but chose to leave the answer since some people may end up here while searching for that.

---

No, an object could be attached to multiple properties, so it has no way of knowing its name.

var obj = {a:1};
var a = {x: obj, y: obj}

What would obj's name be?

Are you sure you don't just want the property name from the for loop?

for (var propName in obj) {
  console.log("Iterating through prop with name", propName, " its value is ", obj[propName])
}

Answer 4

you can easily iterate in objects

eg: if the object is var a = {a:'apple', b:'ball', c:'cat', d:'doll', e:'elephant'};

Object.keys(a).forEach(key => {
   console.log(key) // returns the keys in an object
   console.log(a[key])  // returns the appropriate value 
})

Answer 5

Other than "Object.keys( obj )", we have very simple "for...in" loop - which loops over enumerable property names of an object.

const obj = {"fName":"John","lName":"Doe"};

for (const key in obj) {
    //This will give key
      console.log(key);
    //This will give value
    console.log(obj[key]);
    
}

Answer 6

for direct access a object property by position... generally usefull for property [0]... so it holds info about the further... or in node.js 'require.cache[0]' for the first loaded external module, etc. etc.

Object.keys( myObject )[ 0 ]
Object.keys( myObject )[ 1 ]
...
Object.keys( myObject )[ n ]

Answer 7

To get the property of the object or the "array key" or "array index" depending on what your native language is..... Use the Object.keys() method.

Important, this is only compatible with "Modern browsers":

So if your object is called, myObject...

var c = 0;
for(c in myObject) {
    console.log(Object.keys(myObject[c]));
}

Walla! This will definitely work in the latest firefox and ie11 and chrome...

Here is some documentation at MDN https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

Answer 8

IN ES5

E.G. you have this kind of object:

var ELEMENTS = {
    STEP_ELEMENT: { ID: "0", imageName: "el_0.png" },
    GREEN_ELEMENT: { ID: "1", imageName: "el_1.png" },
    BLUE_ELEMENT: { ID: "2", imageName: "el_2.png" },
    ORANGE_ELEMENT: { ID: "3", imageName: "el_3.png" },
    PURPLE_ELEMENT: { ID: "4", imageName: "el_4.png" },
    YELLOW_ELEMENT: { ID: "5", imageName: "el_5.png" }
};

And now if you want to have a function that if you pass '0' as a param - to get 'STEP_ELEMENT', if '2' to get 'BLUE_ELEMENT' and so for

function(elementId) {
    var element = null;

    Object.keys(ELEMENTS).forEach(function(key) {
        if(ELEMENTS[key].ID === elementId.toString()){
            element = key;
            return;
        }    
    });

    return element;
}

This is probably not the best solution to the problem but its good to give you an idea how to do it.

Cheers.

Answer 9

As of 2018 , You can make use of Object.getOwnPropertyNames() as described in Developer Mozilla Documentation

const object1 = {
  a: 1,
  b: 2,
  c: 3
};

console.log(Object.getOwnPropertyNames(object1));
// expected output: Array ["a", "b", "c"]

Answer 10

Using Object.keys() function for acquiring properties from an Object, and it can help search property by name, for example:

const Products = function(){
    this.Product = "Product A";
    this.Price = 9.99;
    this.Quantity = 112;
};

// Simple find function case insensitive
let findPropByName = function(data, propertyName){
 let props = [];
 Object.keys(data).forEach(element => {
    return props.push(element.toLowerCase());
  });
  console.log(props);
  let i = props.indexOf(propertyName.toLowerCase());

  if(i > -1){
    return props[i];
  }
  return false;
};

// calling the function
let products = new Products();
console.log(findPropByName(products, 'quantity'));

Answer 11

When you do the for/in loop you put up first, i is the property name. So you have the property name, i, and access the value by doing myObject[i].

Answer 12

These solutions work too.

// Solution One
function removeProperty(obj, prop) {
  var bool;
  var keys = Object.keys(obj);
  for (var i = 0; i < keys.length; i++) {
    if (keys[i] === prop) {
      delete obj[prop];
      bool = true;
    } 
  }
  return Boolean(bool);
}


//Solution two
function removeProperty(obj, prop) {
  var bool;
  if (obj.hasOwnProperty(prop)) {
      bool = true;
      delete obj[prop];
  }
  return Boolean(bool);
}

Answer 13

Quick & dirty:

function getObjName(obj) {
  return (wrap={obj}) && eval('for(p in obj){p}') && (wrap=null);
}