JavaScript Get Object Key Name

Javascript get object key name

This might be better understood if you modified the wording up a bit:

var buttons = {
  foo: 'bar',
  fiz: 'buz'
};

for ( var property in buttons ) {
  console.log( property ); // Outputs: foo, fiz or fiz, foo
}

Note here that you're iterating over the properties of the object, using property as a reference to each during each subsequent cycle.

MSDN says of for ( variable in [object | array ] ) the following:

Before each iteration of a loop, variable is assigned the next property name of object or the next element index of array. You can then use it in any of the statements inside the loop to reference the property of object or the element of array.

Note also that the property order of an object is not constant, and can change, unlike the index order of an array. That might come in handy.

Getting the object's property name

Use Object.keys():

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

Get the key names of the object with value equals to something

ES6+ in one line

let key = Object.keys(obj).find(k=> obj[k] === value);

Get all the keys with

let keys = Object.keys(obj).filter( k => obj[k] === value);

How to get a key in a JavaScript object by its value?

function getKeyByValue(object, value) {
  return Object.keys(object).find(key => object[key] === value);
}

ES6, no prototype mutations or external libraries.

Example,

function getKeyByValue(object, value) {  return Object.keys(object).find(key => object[key] === value);}

const map = {"first" : "1", "second" : "2"};console.log(getKeyByValue(map,"2"));

Javascript get Object property Name

If you know for sure that there's always going to be exactly one key in the object, then you can use Object.keys:

theTypeIs = Object.keys(myVar)[0];

JS get key name using map()

const obj = {
    "thumbnail": {
        "height": 150,
        "width": 150,
    },
    "medium": {
        "height": 165,
        "width": 300,
    },
    "large": {
        "height": 352,
        "width": 640,
    }       
}

const retrnArr = Object.keys(obj).map(e =>{
return  { 'value': e , 'label' : e.toUpperCase()}
});
console.log(retrnArr)

Get key name of a javascript object in an array of objects

The documentation for map says:

Creates an array of values by running each element in collection thru
iteratee. The iteratee is invoked with three arguments: (value,
index|key, collection).

As you can see, the second parameter passed to the iteratee is the original key in the collection. So, just add another parameter to the iteratee and use that:

const categoryValues = _.map(groups, (element, name) => {
    return {
        categoryName: name,
        categoryValue: _.reduce(element,(acc, el) => el.value,0),
    };
});

Get the first key name of a JavaScript object

In Javascript you can do the following:

Object.keys(ahash)[0];

JavaScript set object key by variable

You need to make the object first, then use [] to set it.

var key = "happyCount";
var obj = {};

obj[key] = someValueArray;
myArray.push(obj);

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UPDATE 2021:

Computed property names feature was introduced in ECMAScript 2015 (ES6) that allows you to dynamically compute the names of the object properties in JavaScript object literal notation.

const yourKeyVariable = "happyCount";
const someValueArray= [...];

const obj = {
    [yourKeyVariable]: someValueArray,
}

How to get the property name of object and use that property name in javascript

The only error in your code is mapped_errors.{obj_key}.msg. You should be using [] to access the object's property value when you are using a variable to get the key name, as mapped_errors[obj_key].

var mapped_errors = { _id:   { location: 'body',     param: '_id',     value: 123,     msg: '_id is required and must be a string' } };
let obj_key = Object.keys(mapped_errors);console.log(mapped_errors[obj_key].msg);
mapped_errors = { _name:   { location: 'body',     param: '_name',     value: 123,     msg: '_name is required and must be a string' } }     obj_key = Object.keys(mapped_errors);console.log(mapped_errors[obj_key].msg);

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