Variable name as a string in Javascript

Question

Is there a way to get a variable name as a string in Javascript? (like NSStringFromSelector in Cocoa)

I would like to do like this:

var myFirstName = 'John';
alert(variablesName(myFirstName) + ":" + myFirstName);

--> myFirstName:John

---

UPDATE

I'm trying to connect a browser and another program using JavaScript. I would like to send instance names from a browser to another program for callback method:

FooClass = function(){};
FooClass.someMethod = function(json) {
  // Do something
}

instanceA = new FooClass();
instanceB = new FooClass();
doSomethingInAnotherProcess(instanceB); // result will be substituted by using instanceB.someMethod();

...

From another program:

evaluateJavascriptInBrowser("(instanceName).someMethod("resultA");");

In PHP: How to get a variable name as a string in PHP?

Answer 1

You can use the following solution to solve your problem:

const myFirstName = 'John'
Object.keys({myFirstName})[0]

// returns "myFirstName"

Answer 2

Like Seth's answer, but uses Object.keys() instead:

const varToString = varObj => Object.keys(varObj)[0]

const someVar = 42
const displayName = varToString({ someVar })
console.log(displayName)

Answer 3

In ES6, you could write something like:

let myVar = 'something';
let nameObject = {myVar};
let getVarNameFromObject = (nameObject) => {
  for(let varName in nameObject) {
    return varName;
  }
}
let varName = getVarNameFromObject(nameObject);

console.log(varName);

Not really the best looking thing, but it gets the job done.

This leverages ES6's object destructuring.

More info here: https://hacks.mozilla.org/2015/05/es6-in-depth-destructuring/

Answer 4

Typically, you would use a hash table for a situation where you want to map a name to some value, and be able to retrieve both.

var obj = { myFirstName: 'John' };
obj.foo = 'Another name';
for(key in obj)
    console.log(key + ': ' + obj[key]);

Answer 5

Get a string from any valid Javascript (variable, class):

const nameOf = (f) => (f).toString().replace(/[ |\(\)=>]/g,'');

Examples:

nameOf(() => myVariable)             // myVariable
nameOf(() => myVariable.name)        // myVariable.name
nameOf(() => myVariable.name.length) // myVariable.name.length
nameOf(() => myVariable.name[10])    // myVariable.name[10]
nameOf(() => MySuperClass)           // MySuperClass

Answer 6

Probably pop would be better than indexing with [0], for safety (variable might be null).

const myFirstName = 'John'
const variableName = Object.keys({myFirstName}).pop();
console.log(`Variable ${variableName} with value '${myFirstName}'`);

// returns "Variable myFirstName with value 'John'"

Answer 7

var x = 2;
for(o in window){ 
   if(window[o] === x){
      alert(o);
   }
}

However, I think you should do like "karim79"

Answer 8

This works for basic expressions

const nameof = exp => exp.toString().match(/[.](\w+)/)[1];

Example

nameof(() => options.displaySize);

Snippet:

var nameof = function (exp) { return exp.toString().match(/[.](\w+)/)[1]; };
var myFirstName = 'Chuck';
var varname = nameof(function () { return window.myFirstName; });
console.log(varname);

Answer 9

var somefancyvariable = "fancy";
Object.keys({somefancyvariable})[0];

This isn't able to be made into a function as it returns the name of the function's variable.

// THIS DOESN'T WORK
function getVarName(v) {
    return Object.keys({v})[0];
}
// Returns "v"

Edit: Thanks to @Madeo for pointing out how to make this into a function.

function debugVar(varObj) {
    var varName = Object.keys(varObj)[0];
    console.log("Var \"" + varName + "\" has a value of \"" + varObj[varName] + "\"");
}

You will need call the function with a single element array containing the variable. debugVar({somefancyvariable});
Edit: Object.keys can be referenced as just keys in every browser I tested it in but according to the comments it doesn't work everywhere.

Answer 10

Shortest way I have found so far to get the variables name as a string:

const name = obj => Object.keys(obj)[0];

const whatsMyName = "Snoop Doggy Dogg";

console.log( "Variable name is: " + name({ whatsMyName }) );
//result: Variable name is: whatsMyName

Answer 11

Since ECMAScript 5.1 you can use Object.keys to get the names of all properties from an object.

Here is an example:

// Get John’s properties (firstName, lastName)
var john = {firstName: 'John', lastName: 'Doe'};
var properties = Object.keys(john);

// Show John’s properties
var message = 'John’s properties are: ' + properties.join(', ');
document.write(message);

Answer 12

best way using Object.keys();

example : for getting multi variables names in global scope

// multi variables for testing
var x = 5 , b = true , m = 6 , v = "str";

// pass all variables you want in object
function getVarsNames(v = {}){
  // getting keys or names !
  let names = Object.keys(v);
  // return array contain all names of variables 
  return names;
}

// testing if that work or not 
let VarsNames = getVarsNames({x , b , m , v});

console.log(VarsNames); // output is array [x , b , m , v]

Answer 13

For those who would like to print variableName and variableValue for debugging purposes, here is a function:

const printNameValue = (v)=> {
  var varName = (v).toString().replace(/[ |\(\)=>]/g, '')
  var varValue = (v)()
  // neat : console.log(varName,varValue);
  // with some coloring  : 
  console.log("\033[1;96m[\033[1;33m " + varName + " :\033[0;0m " + varValue+"\033[1;96m ]\033[0;0m");
}

Example:

const myNiceVariable = 1234
call:
printNameValue(()=> myNiceVariable )
result:

Answer 14

This worked using Internet Explorer (9, 10 and 11), Google Chrome 5:

   
var myFirstName = "Danilo";
var varName = Object.keys({myFirstName:0})[0];
console.log(varName);

Browser compatibility table:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

Answer 15

When having a function write a function that changes different global variables values it is not always myfirstname it is whatever happens to be passing through. Try this worked for me.

_{Run in jsfiddle}

var jack = 'jill';
function window_getVarName(what)
{
  for (var name in window)
  {
    if (window[name]==what)
    return(name);
  }
  return("");
}
document.write(window_getVarName(jack));

Will write to the window 'jack'.

Answer 16

I needed this, don't want to use objects, and came up with the following solution, turning the question around.

Instead of converting the variable name into a string, I convert a string into a variable.

This only works if the variable name is known of course.

Take this:

var height = 120;
testAlert(height);

This should display:

height: 120

This can be done like this:

function testAlert(ta)
{
    a = window[ta];
    alert(ta + ': ' + a); 
}

var height = 120;
testAlert("height");
// displays: height: 120

So I use the string "height" and turn that into a variable height using the window[] command.

Answer 17

You can reflect on types in javascript and get the name of properties and methods but what you need is sth like Lambda Expressions Trees in .NET, I think it's not be possible due to dynamic nature and lack of static type system in javascript.

Answer 18

I've created this function based on JSON as someone suggested, works fine for my debug needs

function debugVar(varNames){
let strX = "";
function replacer(key, value){
    if (value === undefined){return "undef"}
    return value
    }    
for (let arg of arguments){
let lastChar;
    if (typeof arg!== "string"){
        let _arg = JSON.stringify(arg, replacer);
        _arg = _arg.replace('{',"");
        _arg = _arg.replace('}',"");            
        _arg = _arg.replace(/:/g,"=");
        _arg = _arg.replace(/"/g,"");
        strX+=_arg;
    }else{
    strX+=arg;
    lastChar = arg[arg.length-1];
    }
    if (arg!==arguments[arguments.length-1]&&lastChar!==":"){strX+=" "};
}
console.log(strX)    
}
let a = 42, b = 3, c;
debugVar("Begin:",{a,b,c},"end")

Answer 19

If you're looking for something quick and dirty, this might work:

var zox = 150;

cl("zox");

function cl(c) {
    console.log(c + ': ' + this[c]); // zox: 150    
}

Answer 20

No, there is not.
Besides, if you can write variablesName(myFirstName), you already know the variable name ("myFirstName").