Is there a JavaScript equivalent of Java's class.getName()?
This question is related to
javascript
Ok, folks I've been slowly building a catch all method for this over some years lol! The trick is to:
For an example (or to see how I dealt with the problem) look at the following code on github: https://github.com/elycruz/sjljs/blob/master/src/sjl/sjl.js and search for:
classOf =,
classOfIs =, and or
defineSubClass = (without the backticks (`)).
As you can see I have some mechanisms in place to force classOf to always give me the classes/constructors type name regardless of whether it is a primitive, a user defined class, a value created using a native constructor, Null, NaN, etc.. For every single javascript value I will get it's unique type name from the classOf function. In addition I can pass in actual constructors into sjl.classOfIs to check a value's type in addition to being able to pass in it's type name as well! So for example:
``` // Please forgive long namespaces! I had no idea on the impact until after using them for a while (they suck haha)
var SomeCustomClass = sjl.package.stdlib.Extendable.extend({
constructor: function SomeCustomClass () {},
// ...
}),
HelloIterator = sjl.ns.stdlib.Iterator.extend(
function HelloIterator () {},
{ /* ... methods here ... */ },
{ /* ... static props/methods here ... */ }
),
helloIt = new HelloIterator();
sjl.classOfIs(new SomeCustomClass(), SomeCustomClass) === true; // `true`
sjl.classOfIs(helloIt, HelloIterator) === true; // `true`
var someString = 'helloworld';
sjl.classOfIs(someString, String) === true; // `true`
sjl.classOfIs(99, Number) === true; // true
sjl.classOf(NaN) === 'NaN'; // true
sjl.classOf(new Map()) === 'Map';
sjl.classOf(new Set()) === 'Set';
sjl.classOfIs([1, 2, 4], Array) === true; // `true`
// etc..
// Also optionally the type you want to check against could be the type's name
sjl.classOfIs(['a', 'b', 'c'], 'Array') === true; // `true`!
sjl.classOfIs(helloIt, 'HelloIterator') === true; // `true`!
```
If you are interested in reading more on how I use the setup mentioned above take a look at the repo: https://github.com/elycruz/sjljs
Also books with content on the subject: - "JavaScript Patterns" by Stoyan Stefanov. - "Javascript - The Definitive Guide." by David Flanagan. - and many others.. (search le` web).
Also you can quickly test the features I'm talking about here: - http://sjljs.elycruz.com/0.5.18/tests/for-browser/ (also the 0.5.18 path in the url has the sources from github on there minus the node_modules and such).
Happy Coding!
You can use the "instanceof" operator to determine if an object is an instance of a certain class or not. If you do not know the name of an object's type, you can use its constructor property. The constructor property of objects, is a reference to the function that is used to initialize them. Example:
function Circle (x,y,radius) {
this._x = x;
this._y = y;
this._radius = raduius;
}
var c1 = new Circle(10,20,5);
Now c1.constructor is a reference to the Circle() function.
You can alsow use the typeof operator, but the typeof operator shows limited information. One solution is to use the toString() method of the Object global object. For example if you have an object, say myObject, you can use the toString() method of the global Object to determine the type of the class of myObject. Use this:
Object.prototype.toString.apply(myObject);
Use class.name. This also works with function.name.
class TestA {}
console.log(TestA.name); // "TestA"
function TestB() {}
console.log(TestB.name); // "TestB"
function getType(entity){
var x = Object.prototype.toString.call(entity)
return x.split(" ")[1].split(']')[0].toLowerCase()
}
function checkType(entity, type){
return getType(entity) === type
}
Jason Bunting's answer gave me enough of a clue to find what I needed:
<<Object instance>>.constructor.name
So, for example, in the following piece of code:
function MyObject() {}
var myInstance = new MyObject();
myInstance.constructor.name would return "MyObject".
You can use the "instanceof" operator to determine if an object is an instance of a certain class or not. If you do not know the name of an object's type, you can use its constructor property. The constructor property of objects, is a reference to the function that is used to initialize them. Example:
function Circle (x,y,radius) {
this._x = x;
this._y = y;
this._radius = raduius;
}
var c1 = new Circle(10,20,5);
Now c1.constructor is a reference to the Circle() function.
You can alsow use the typeof operator, but the typeof operator shows limited information. One solution is to use the toString() method of the Object global object. For example if you have an object, say myObject, you can use the toString() method of the global Object to determine the type of the class of myObject. Use this:
Object.prototype.toString.apply(myObject);
I was actually looking for a similar thing and came across this question. Here is how I get types: jsfiddle
var TypeOf = function ( thing ) {
var typeOfThing = typeof thing;
if ( 'object' === typeOfThing ) {
typeOfThing = Object.prototype.toString.call( thing );
if ( '[object Object]' === typeOfThing ) {
if ( thing.constructor.name ) {
return thing.constructor.name;
}
else if ( '[' === thing.constructor.toString().charAt(0) ) {
typeOfThing = typeOfThing.substring( 8,typeOfThing.length - 1 );
}
else {
typeOfThing = thing.constructor.toString().match( /function\s*(\w+)/ );
if ( typeOfThing ) {
return typeOfThing[1];
}
else {
return 'Function';
}
}
}
else {
typeOfThing = typeOfThing.substring( 8,typeOfThing.length - 1 );
}
}
return typeOfThing.charAt(0).toUpperCase() + typeOfThing.slice(1);
}
Use constructor.name when you can, and regex function when I can't.
Function.prototype.getName = function(){
if (typeof this.name != 'undefined')
return this.name;
else
return /function (.+)\(/.exec(this.toString())[1];
};
The closest you can get is typeof, but it only returns "object" for any sort of custom type. For those, see Jason Bunting.
Edit, Jason's deleted his post for some reason, so just use Object's constructor property.
Say you have var obj;
If you just want the name of obj's type, like "Object", "Array", or "String", you can use this:
Object.prototype.toString.call(obj).split(' ')[1].replace(']', '');
A little trick I use:
function Square(){
this.className = "Square";
this.corners = 4;
}
var MySquare = new Square();
console.log(MySquare.className); // "Square"
Here is a solution that I have come up with that solves the shortcomings of instanceof. It can check an object's types from cross-windows and cross-frames and doesn't have problems with primitive types.
function getType(o) {
return Object.prototype.toString.call(o).match(/^\[object\s(.*)\]$/)[1];
}
function isInstance(obj, type) {
var ret = false,
isTypeAString = getType(type) == "String",
functionConstructor, i, l, typeArray, context;
if (!isTypeAString && getType(type) != "Function") {
throw new TypeError("type argument must be a string or function");
}
if (obj !== undefined && obj !== null && obj.constructor) {
//get the Function constructor
functionConstructor = obj.constructor;
while (functionConstructor != functionConstructor.constructor) {
functionConstructor = functionConstructor.constructor;
}
//get the object's window
context = functionConstructor == Function ? self : functionConstructor("return window")();
//get the constructor for the type
if (isTypeAString) {
//type is a string so we'll build the context (window.Array or window.some.Type)
for (typeArray = type.split("."), i = 0, l = typeArray.length; i < l && context; i++) {
context = context[typeArray[i]];
}
} else {
//type is a function so execute the function passing in the object's window
//the return should be a constructor
context = type(context);
}
//check if the object is an instance of the constructor
if (context) {
ret = obj instanceof context;
if (!ret && (type == "Number" || type == "String" || type == "Boolean")) {
ret = obj.constructor == context
}
}
}
return ret;
}
isInstance requires two parameters: an object and a type. The real trick to how it works is that it checks if the object is from the same window and if not gets the object's window.
Examples:
isInstance([], "Array"); //true
isInstance("some string", "String"); //true
isInstance(new Object(), "Object"); //true
function Animal() {}
function Dog() {}
Dog.prototype = new Animal();
isInstance(new Dog(), "Dog"); //true
isInstance(new Dog(), "Animal"); //true
isInstance(new Dog(), "Object"); //true
isInstance(new Animal(), "Dog"); //false
The type argument can also be a callback function which returns a constructor. The callback function will receive one parameter which is the window of the provided object.
Examples:
//"Arguments" type check
var args = (function() {
return arguments;
}());
isInstance(args, function(w) {
return w.Function("return arguments.constructor")();
}); //true
//"NodeList" type check
var nl = document.getElementsByTagName("*");
isInstance(nl, function(w) {
return w.document.getElementsByTagName("bs").constructor;
}); //true
One thing to keep in mind is that IE < 9 does not provide the constructor on all objects so the above test for NodeList would return false and also a isInstance(alert, "Function") would return false.
You can use the instanceof operator to see if an object is an instance of another, but since there are no classes, you can't get a class name.
The kind() function from Agave.JS will return:
It works on all JS objects and primitives, regardless of how they were created, and doesn't have any surprises. Examples:
kind(37) === 'Number'
kind(3.14) === 'Number'
kind(Math.LN2) === 'Number'
kind(Infinity) === 'Number'
kind(Number(1)) === 'Number'
kind(new Number(1)) === 'Number'
kind(NaN) === 'NaN'
kind('') === 'String'
kind('bla') === 'String'
kind(String("abc")) === 'String'
kind(new String("abc")) === 'String'
kind(true) === 'Boolean'
kind(false) === 'Boolean'
kind(new Boolean(true)) === 'Boolean'
kind([1, 2, 4]) === 'Array'
kind(new Array(1, 2, 3)) === 'Array'
kind({a:1}) === 'Object'
kind(new Object()) === 'Object'
kind(new Date()) === 'Date'
kind(function(){}) === 'Function'
kind(new Function("console.log(arguments)")) === 'Function'
kind(Math.sin) === 'Function'
kind(undefined) === 'undefined'
kind(null) === 'null'
Ok, folks I've been slowly building a catch all method for this over some years lol! The trick is to:
For an example (or to see how I dealt with the problem) look at the following code on github: https://github.com/elycruz/sjljs/blob/master/src/sjl/sjl.js and search for:
classOf =,
classOfIs =, and or
defineSubClass = (without the backticks (`)).
As you can see I have some mechanisms in place to force classOf to always give me the classes/constructors type name regardless of whether it is a primitive, a user defined class, a value created using a native constructor, Null, NaN, etc.. For every single javascript value I will get it's unique type name from the classOf function. In addition I can pass in actual constructors into sjl.classOfIs to check a value's type in addition to being able to pass in it's type name as well! So for example:
``` // Please forgive long namespaces! I had no idea on the impact until after using them for a while (they suck haha)
var SomeCustomClass = sjl.package.stdlib.Extendable.extend({
constructor: function SomeCustomClass () {},
// ...
}),
HelloIterator = sjl.ns.stdlib.Iterator.extend(
function HelloIterator () {},
{ /* ... methods here ... */ },
{ /* ... static props/methods here ... */ }
),
helloIt = new HelloIterator();
sjl.classOfIs(new SomeCustomClass(), SomeCustomClass) === true; // `true`
sjl.classOfIs(helloIt, HelloIterator) === true; // `true`
var someString = 'helloworld';
sjl.classOfIs(someString, String) === true; // `true`
sjl.classOfIs(99, Number) === true; // true
sjl.classOf(NaN) === 'NaN'; // true
sjl.classOf(new Map()) === 'Map';
sjl.classOf(new Set()) === 'Set';
sjl.classOfIs([1, 2, 4], Array) === true; // `true`
// etc..
// Also optionally the type you want to check against could be the type's name
sjl.classOfIs(['a', 'b', 'c'], 'Array') === true; // `true`!
sjl.classOfIs(helloIt, 'HelloIterator') === true; // `true`!
```
If you are interested in reading more on how I use the setup mentioned above take a look at the repo: https://github.com/elycruz/sjljs
Also books with content on the subject: - "JavaScript Patterns" by Stoyan Stefanov. - "Javascript - The Definitive Guide." by David Flanagan. - and many others.. (search le` web).
Also you can quickly test the features I'm talking about here: - http://sjljs.elycruz.com/0.5.18/tests/for-browser/ (also the 0.5.18 path in the url has the sources from github on there minus the node_modules and such).
Happy Coding!
Jason Bunting's answer gave me enough of a clue to find what I needed:
<<Object instance>>.constructor.name
So, for example, in the following piece of code:
function MyObject() {}
var myInstance = new MyObject();
myInstance.constructor.name would return "MyObject".
Using Object.prototype.toString
It turns out, as this post details, you can use Object.prototype.toString - the low level and generic implementation of toString - to get the type for all built-in types
Object.prototype.toString.call('abc') // [object String]
Object.prototype.toString.call(/abc/) // [object RegExp]
Object.prototype.toString.call([1,2,3]) // [object Array]
One could write a short helper function such as
function type(obj){
return Object.prototype.toString.call(obj]).match(/\s\w+/)[0].trim()
}
return [object String] as String
return [object Number] as Number
return [object Object] as Object
return [object Undefined] as Undefined
return [object Function] as Function
You can use the "instanceof" operator to determine if an object is an instance of a certain class or not. If you do not know the name of an object's type, you can use its constructor property. The constructor property of objects, is a reference to the function that is used to initialize them. Example:
function Circle (x,y,radius) {
this._x = x;
this._y = y;
this._radius = raduius;
}
var c1 = new Circle(10,20,5);
Now c1.constructor is a reference to the Circle() function.
You can alsow use the typeof operator, but the typeof operator shows limited information. One solution is to use the toString() method of the Object global object. For example if you have an object, say myObject, you can use the toString() method of the global Object to determine the type of the class of myObject. Use this:
Object.prototype.toString.apply(myObject);
If anyone was looking for a solution which is working with jQuery, here is the adjusted wiki code (the original breaks jQuery).
Object.defineProperty(Object.prototype, "getClassName", {
value: function() {
var funcNameRegex = /function (.{1,})\(/;
var results = (funcNameRegex).exec((this).constructor.toString());
return (results && results.length > 1) ? results[1] : "";
}
});
For of those of you reading this and want a simple solution that works fairly well and has been tested:
const getTypeName = (thing) => {
const name = typeof thing
if (name !== 'object') return name
if (thing instanceof Error) return 'error'
if (!thing) return 'null'
return ({}).toString.call(thing).match(/\s([a-zA-Z]+)/)[1].toLowerCase()
}
To get insight on why this works, checkout the polyfill documentation for Array.isArray(): https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray#polyfill
Use class.name. This also works with function.name.
class TestA {}
console.log(TestA.name); // "TestA"
function TestB() {}
console.log(TestB.name); // "TestB"
Using Object.prototype.toString
It turns out, as this post details, you can use Object.prototype.toString - the low level and generic implementation of toString - to get the type for all built-in types
Object.prototype.toString.call('abc') // [object String]
Object.prototype.toString.call(/abc/) // [object RegExp]
Object.prototype.toString.call([1,2,3]) // [object Array]
One could write a short helper function such as
function type(obj){
return Object.prototype.toString.call(obj]).match(/\s\w+/)[0].trim()
}
return [object String] as String
return [object Number] as Number
return [object Object] as Object
return [object Undefined] as Undefined
return [object Function] as Function
To be precise, I think OP asked for a function that retrieves the constructor name for a particular object. In terms of Javascript, object does not have a type but is a type of and in itself. However, different objects can have different constructors.
Object.prototype.getConstructorName = function () {
var str = (this.prototype ? this.prototype.constructor : this.constructor).toString();
var cname = str.match(/function\s(\w*)/)[1];
var aliases = ["", "anonymous", "Anonymous"];
return aliases.indexOf(cname) > -1 ? "Function" : cname;
}
new Array().getConstructorName(); // returns "Array"
(function () {})().getConstructorName(); // returns "Function"
Note: the below example is deprecated.
A blog post linked by Christian Sciberras contains a good example on how to do it. Namely, by extending the Object prototype:
if (!Object.prototype.getClassName) {
Object.prototype.getClassName = function () {
return Object.prototype.toString.call(this).match(/^\[object\s(.*)\]$/)[1];
}
}
var test = [1,2,3,4,5];
alert(test.getClassName()); // returns Array
The kind() function from Agave.JS will return:
It works on all JS objects and primitives, regardless of how they were created, and doesn't have any surprises. Examples:
kind(37) === 'Number'
kind(3.14) === 'Number'
kind(Math.LN2) === 'Number'
kind(Infinity) === 'Number'
kind(Number(1)) === 'Number'
kind(new Number(1)) === 'Number'
kind(NaN) === 'NaN'
kind('') === 'String'
kind('bla') === 'String'
kind(String("abc")) === 'String'
kind(new String("abc")) === 'String'
kind(true) === 'Boolean'
kind(false) === 'Boolean'
kind(new Boolean(true)) === 'Boolean'
kind([1, 2, 4]) === 'Array'
kind(new Array(1, 2, 3)) === 'Array'
kind({a:1}) === 'Object'
kind(new Object()) === 'Object'
kind(new Date()) === 'Date'
kind(function(){}) === 'Function'
kind(new Function("console.log(arguments)")) === 'Function'
kind(Math.sin) === 'Function'
kind(undefined) === 'undefined'
kind(null) === 'null'
Lodash has many isMethods so if you're using Lodash maybe a mixin like this can be useful:
// Mixin for identifying a Javascript Object
_.mixin({
'identify' : function(object) {
var output;
var isMethods = ['isArguments', 'isArray', 'isArguments', 'isBoolean', 'isDate', 'isArguments',
'isElement', 'isError', 'isFunction', 'isNaN', 'isNull', 'isNumber',
'isPlainObject', 'isRegExp', 'isString', 'isTypedArray', 'isUndefined', 'isEmpty', 'isObject']
this.each(isMethods, function (method) {
if (this[method](object)) {
output = method;
return false;
}
}.bind(this));
return output;
}
});
It adds a method to lodash called "identify" which works as follow:
console.log(_.identify('hello friend')); // isString
The closest you can get is typeof, but it only returns "object" for any sort of custom type. For those, see Jason Bunting.
Edit, Jason's deleted his post for some reason, so just use Object's constructor property.
You can use the instanceof operator to see if an object is an instance of another, but since there are no classes, you can't get a class name.
Use constructor.name when you can, and regex function when I can't.
Function.prototype.getName = function(){
if (typeof this.name != 'undefined')
return this.name;
else
return /function (.+)\(/.exec(this.toString())[1];
};
Jason Bunting's answer gave me enough of a clue to find what I needed:
<<Object instance>>.constructor.name
So, for example, in the following piece of code:
function MyObject() {}
var myInstance = new MyObject();
myInstance.constructor.name would return "MyObject".
Here is an implementation based on the accepted answer:
/**_x000D_
* Returns the name of an object's type._x000D_
*_x000D_
* If the input is undefined, returns "Undefined"._x000D_
* If the input is null, returns "Null"._x000D_
* If the input is a boolean, returns "Boolean"._x000D_
* If the input is a number, returns "Number"._x000D_
* If the input is a string, returns "String"._x000D_
* If the input is a named function or a class constructor, returns "Function"._x000D_
* If the input is an anonymous function, returns "AnonymousFunction"._x000D_
* If the input is an arrow function, returns "ArrowFunction"._x000D_
* If the input is a class instance, returns "Object"._x000D_
*_x000D_
* @param {Object} object an object_x000D_
* @return {String} the name of the object's class_x000D_
* @see <a href="https://stackoverflow.com/a/332429/14731">https://stackoverflow.com/a/332429/14731</a>_x000D_
* @see getFunctionName_x000D_
* @see getObjectClass _x000D_
*/_x000D_
function getTypeName(object)_x000D_
{_x000D_
const objectToString = Object.prototype.toString.call(object).slice(8, -1);_x000D_
if (objectToString === "Function")_x000D_
{_x000D_
const instanceToString = object.toString();_x000D_
if (instanceToString.indexOf(" => ") != -1)_x000D_
return "ArrowFunction";_x000D_
const getFunctionName = /^function ([^(]+)\(/;_x000D_
const match = instanceToString.match(getFunctionName);_x000D_
if (match === null)_x000D_
return "AnonymousFunction";_x000D_
return "Function";_x000D_
}_x000D_
// Built-in types (e.g. String) or class instances_x000D_
return objectToString;_x000D_
};_x000D_
_x000D_
/**_x000D_
* Returns the name of a function._x000D_
*_x000D_
* If the input is an anonymous function, returns ""._x000D_
* If the input is an arrow function, returns "=>"._x000D_
*_x000D_
* @param {Function} fn a function_x000D_
* @return {String} the name of the function_x000D_
* @throws {TypeError} if {@code fn} is not a function_x000D_
* @see getTypeName_x000D_
*/_x000D_
function getFunctionName(fn)_x000D_
{_x000D_
try_x000D_
{_x000D_
const instanceToString = fn.toString();_x000D_
if (instanceToString.indexOf(" => ") != -1)_x000D_
return "=>";_x000D_
const getFunctionName = /^function ([^(]+)\(/;_x000D_
const match = instanceToString.match(getFunctionName);_x000D_
if (match === null)_x000D_
{_x000D_
const objectToString = Object.prototype.toString.call(fn).slice(8, -1);_x000D_
if (objectToString === "Function")_x000D_
return "";_x000D_
throw TypeError("object must be a Function.\n" +_x000D_
"Actual: " + getTypeName(fn));_x000D_
}_x000D_
return match[1];_x000D_
}_x000D_
catch (e)_x000D_
{_x000D_
throw TypeError("object must be a Function.\n" +_x000D_
"Actual: " + getTypeName(fn));_x000D_
}_x000D_
};_x000D_
_x000D_
/**_x000D_
* @param {Object} object an object_x000D_
* @return {String} the name of the object's class_x000D_
* @throws {TypeError} if {@code object} is not an Object_x000D_
* @see getTypeName_x000D_
*/_x000D_
function getObjectClass(object)_x000D_
{_x000D_
const getFunctionName = /^function ([^(]+)\(/;_x000D_
const result = object.constructor.toString().match(getFunctionName)[1];_x000D_
if (result === "Function")_x000D_
{_x000D_
throw TypeError("object must be an Object.\n" +_x000D_
"Actual: " + getTypeName(object));_x000D_
}_x000D_
return result;_x000D_
};_x000D_
_x000D_
_x000D_
function UserFunction()_x000D_
{_x000D_
}_x000D_
_x000D_
function UserClass()_x000D_
{_x000D_
}_x000D_
_x000D_
let anonymousFunction = function()_x000D_
{_x000D_
};_x000D_
_x000D_
let arrowFunction = i => i + 1;_x000D_
_x000D_
console.log("getTypeName(undefined): " + getTypeName(undefined));_x000D_
console.log("getTypeName(null): " + getTypeName(null));_x000D_
console.log("getTypeName(true): " + getTypeName(true));_x000D_
console.log("getTypeName(5): " + getTypeName(5));_x000D_
console.log("getTypeName(\"text\"): " + getTypeName("text"));_x000D_
console.log("getTypeName(userFunction): " + getTypeName(UserFunction));_x000D_
console.log("getFunctionName(userFunction): " + getFunctionName(UserFunction));_x000D_
console.log("getTypeName(anonymousFunction): " + getTypeName(anonymousFunction));_x000D_
console.log("getFunctionName(anonymousFunction): " + getFunctionName(anonymousFunction));_x000D_
console.log("getTypeName(arrowFunction): " + getTypeName(arrowFunction));_x000D_
console.log("getFunctionName(arrowFunction): " + getFunctionName(arrowFunction));_x000D_
//console.log("getFunctionName(userClass): " + getFunctionName(new UserClass()));_x000D_
console.log("getTypeName(userClass): " + getTypeName(new UserClass()));_x000D_
console.log("getObjectClass(userClass): " + getObjectClass(new UserClass()));_x000D_
//console.log("getObjectClass(userFunction): " + getObjectClass(UserFunction));_x000D_
//console.log("getObjectClass(userFunction): " + getObjectClass(anonymousFunction));_x000D_
//console.log("getObjectClass(arrowFunction): " + getObjectClass(arrowFunction));_x000D_
console.log("getTypeName(nativeObject): " + getTypeName(navigator.mediaDevices.getUserMedia));_x000D_
console.log("getFunctionName(nativeObject): " + getFunctionName(navigator.mediaDevices.getUserMedia));We only use the constructor property when we have no other choice.
The closest you can get is typeof, but it only returns "object" for any sort of custom type. For those, see Jason Bunting.
Edit, Jason's deleted his post for some reason, so just use Object's constructor property.
To be precise, I think OP asked for a function that retrieves the constructor name for a particular object. In terms of Javascript, object does not have a type but is a type of and in itself. However, different objects can have different constructors.
Object.prototype.getConstructorName = function () {
var str = (this.prototype ? this.prototype.constructor : this.constructor).toString();
var cname = str.match(/function\s(\w*)/)[1];
var aliases = ["", "anonymous", "Anonymous"];
return aliases.indexOf(cname) > -1 ? "Function" : cname;
}
new Array().getConstructorName(); // returns "Array"
(function () {})().getConstructorName(); // returns "Function"
Note: the below example is deprecated.
A blog post linked by Christian Sciberras contains a good example on how to do it. Namely, by extending the Object prototype:
if (!Object.prototype.getClassName) {
Object.prototype.getClassName = function () {
return Object.prototype.toString.call(this).match(/^\[object\s(.*)\]$/)[1];
}
}
var test = [1,2,3,4,5];
alert(test.getClassName()); // returns Array
You should use somevar.constructor.name like a:
_x000D_
const getVariableType = a => a.constructor.name.toLowerCase();_x000D_
_x000D_
const d = new Date();_x000D_
const res1 = getVariableType(d); // 'date'_x000D_
const num = 5;_x000D_
const res2 = getVariableType(num); // 'number'_x000D_
const fn = () => {};_x000D_
const res3 = getVariableType(fn); // 'function'_x000D_
_x000D_
console.log(res1); // 'date'_x000D_
console.log(res2); // 'number'_x000D_
console.log(res3); // 'function'You can use the instanceof operator to see if an object is an instance of another, but since there are no classes, you can't get a class name.
For of those of you reading this and want a simple solution that works fairly well and has been tested:
const getTypeName = (thing) => {
const name = typeof thing
if (name !== 'object') return name
if (thing instanceof Error) return 'error'
if (!thing) return 'null'
return ({}).toString.call(thing).match(/\s([a-zA-Z]+)/)[1].toLowerCase()
}
To get insight on why this works, checkout the polyfill documentation for Array.isArray(): https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray#polyfill
Here is an implementation based on the accepted answer:
/**_x000D_
* Returns the name of an object's type._x000D_
*_x000D_
* If the input is undefined, returns "Undefined"._x000D_
* If the input is null, returns "Null"._x000D_
* If the input is a boolean, returns "Boolean"._x000D_
* If the input is a number, returns "Number"._x000D_
* If the input is a string, returns "String"._x000D_
* If the input is a named function or a class constructor, returns "Function"._x000D_
* If the input is an anonymous function, returns "AnonymousFunction"._x000D_
* If the input is an arrow function, returns "ArrowFunction"._x000D_
* If the input is a class instance, returns "Object"._x000D_
*_x000D_
* @param {Object} object an object_x000D_
* @return {String} the name of the object's class_x000D_
* @see <a href="https://stackoverflow.com/a/332429/14731">https://stackoverflow.com/a/332429/14731</a>_x000D_
* @see getFunctionName_x000D_
* @see getObjectClass _x000D_
*/_x000D_
function getTypeName(object)_x000D_
{_x000D_
const objectToString = Object.prototype.toString.call(object).slice(8, -1);_x000D_
if (objectToString === "Function")_x000D_
{_x000D_
const instanceToString = object.toString();_x000D_
if (instanceToString.indexOf(" => ") != -1)_x000D_
return "ArrowFunction";_x000D_
const getFunctionName = /^function ([^(]+)\(/;_x000D_
const match = instanceToString.match(getFunctionName);_x000D_
if (match === null)_x000D_
return "AnonymousFunction";_x000D_
return "Function";_x000D_
}_x000D_
// Built-in types (e.g. String) or class instances_x000D_
return objectToString;_x000D_
};_x000D_
_x000D_
/**_x000D_
* Returns the name of a function._x000D_
*_x000D_
* If the input is an anonymous function, returns ""._x000D_
* If the input is an arrow function, returns "=>"._x000D_
*_x000D_
* @param {Function} fn a function_x000D_
* @return {String} the name of the function_x000D_
* @throws {TypeError} if {@code fn} is not a function_x000D_
* @see getTypeName_x000D_
*/_x000D_
function getFunctionName(fn)_x000D_
{_x000D_
try_x000D_
{_x000D_
const instanceToString = fn.toString();_x000D_
if (instanceToString.indexOf(" => ") != -1)_x000D_
return "=>";_x000D_
const getFunctionName = /^function ([^(]+)\(/;_x000D_
const match = instanceToString.match(getFunctionName);_x000D_
if (match === null)_x000D_
{_x000D_
const objectToString = Object.prototype.toString.call(fn).slice(8, -1);_x000D_
if (objectToString === "Function")_x000D_
return "";_x000D_
throw TypeError("object must be a Function.\n" +_x000D_
"Actual: " + getTypeName(fn));_x000D_
}_x000D_
return match[1];_x000D_
}_x000D_
catch (e)_x000D_
{_x000D_
throw TypeError("object must be a Function.\n" +_x000D_
"Actual: " + getTypeName(fn));_x000D_
}_x000D_
};_x000D_
_x000D_
/**_x000D_
* @param {Object} object an object_x000D_
* @return {String} the name of the object's class_x000D_
* @throws {TypeError} if {@code object} is not an Object_x000D_
* @see getTypeName_x000D_
*/_x000D_
function getObjectClass(object)_x000D_
{_x000D_
const getFunctionName = /^function ([^(]+)\(/;_x000D_
const result = object.constructor.toString().match(getFunctionName)[1];_x000D_
if (result === "Function")_x000D_
{_x000D_
throw TypeError("object must be an Object.\n" +_x000D_
"Actual: " + getTypeName(object));_x000D_
}_x000D_
return result;_x000D_
};_x000D_
_x000D_
_x000D_
function UserFunction()_x000D_
{_x000D_
}_x000D_
_x000D_
function UserClass()_x000D_
{_x000D_
}_x000D_
_x000D_
let anonymousFunction = function()_x000D_
{_x000D_
};_x000D_
_x000D_
let arrowFunction = i => i + 1;_x000D_
_x000D_
console.log("getTypeName(undefined): " + getTypeName(undefined));_x000D_
console.log("getTypeName(null): " + getTypeName(null));_x000D_
console.log("getTypeName(true): " + getTypeName(true));_x000D_
console.log("getTypeName(5): " + getTypeName(5));_x000D_
console.log("getTypeName(\"text\"): " + getTypeName("text"));_x000D_
console.log("getTypeName(userFunction): " + getTypeName(UserFunction));_x000D_
console.log("getFunctionName(userFunction): " + getFunctionName(UserFunction));_x000D_
console.log("getTypeName(anonymousFunction): " + getTypeName(anonymousFunction));_x000D_
console.log("getFunctionName(anonymousFunction): " + getFunctionName(anonymousFunction));_x000D_
console.log("getTypeName(arrowFunction): " + getTypeName(arrowFunction));_x000D_
console.log("getFunctionName(arrowFunction): " + getFunctionName(arrowFunction));_x000D_
//console.log("getFunctionName(userClass): " + getFunctionName(new UserClass()));_x000D_
console.log("getTypeName(userClass): " + getTypeName(new UserClass()));_x000D_
console.log("getObjectClass(userClass): " + getObjectClass(new UserClass()));_x000D_
//console.log("getObjectClass(userFunction): " + getObjectClass(UserFunction));_x000D_
//console.log("getObjectClass(userFunction): " + getObjectClass(anonymousFunction));_x000D_
//console.log("getObjectClass(arrowFunction): " + getObjectClass(arrowFunction));_x000D_
console.log("getTypeName(nativeObject): " + getTypeName(navigator.mediaDevices.getUserMedia));_x000D_
console.log("getFunctionName(nativeObject): " + getFunctionName(navigator.mediaDevices.getUserMedia));We only use the constructor property when we have no other choice.
Jason Bunting's answer gave me enough of a clue to find what I needed:
<<Object instance>>.constructor.name
So, for example, in the following piece of code:
function MyObject() {}
var myInstance = new MyObject();
myInstance.constructor.name would return "MyObject".
If anyone was looking for a solution which is working with jQuery, here is the adjusted wiki code (the original breaks jQuery).
Object.defineProperty(Object.prototype, "getClassName", {
value: function() {
var funcNameRegex = /function (.{1,})\(/;
var results = (funcNameRegex).exec((this).constructor.toString());
return (results && results.length > 1) ? results[1] : "";
}
});
A little trick I use:
function Square(){
this.className = "Square";
this.corners = 4;
}
var MySquare = new Square();
console.log(MySquare.className); // "Square"
function getType(entity){
var x = Object.prototype.toString.call(entity)
return x.split(" ")[1].split(']')[0].toLowerCase()
}
function checkType(entity, type){
return getType(entity) === type
}
The closest you can get is typeof, but it only returns "object" for any sort of custom type. For those, see Jason Bunting.
Edit, Jason's deleted his post for some reason, so just use Object's constructor property.
Lodash has many isMethods so if you're using Lodash maybe a mixin like this can be useful:
// Mixin for identifying a Javascript Object
_.mixin({
'identify' : function(object) {
var output;
var isMethods = ['isArguments', 'isArray', 'isArguments', 'isBoolean', 'isDate', 'isArguments',
'isElement', 'isError', 'isFunction', 'isNaN', 'isNull', 'isNumber',
'isPlainObject', 'isRegExp', 'isString', 'isTypedArray', 'isUndefined', 'isEmpty', 'isObject']
this.each(isMethods, function (method) {
if (this[method](object)) {
output = method;
return false;
}
}.bind(this));
return output;
}
});
It adds a method to lodash called "identify" which works as follow:
console.log(_.identify('hello friend')); // isString
I was actually looking for a similar thing and came across this question. Here is how I get types: jsfiddle
var TypeOf = function ( thing ) {
var typeOfThing = typeof thing;
if ( 'object' === typeOfThing ) {
typeOfThing = Object.prototype.toString.call( thing );
if ( '[object Object]' === typeOfThing ) {
if ( thing.constructor.name ) {
return thing.constructor.name;
}
else if ( '[' === thing.constructor.toString().charAt(0) ) {
typeOfThing = typeOfThing.substring( 8,typeOfThing.length - 1 );
}
else {
typeOfThing = thing.constructor.toString().match( /function\s*(\w+)/ );
if ( typeOfThing ) {
return typeOfThing[1];
}
else {
return 'Function';
}
}
}
else {
typeOfThing = typeOfThing.substring( 8,typeOfThing.length - 1 );
}
}
return typeOfThing.charAt(0).toUpperCase() + typeOfThing.slice(1);
}
Here is a solution that I have come up with that solves the shortcomings of instanceof. It can check an object's types from cross-windows and cross-frames and doesn't have problems with primitive types.
function getType(o) {
return Object.prototype.toString.call(o).match(/^\[object\s(.*)\]$/)[1];
}
function isInstance(obj, type) {
var ret = false,
isTypeAString = getType(type) == "String",
functionConstructor, i, l, typeArray, context;
if (!isTypeAString && getType(type) != "Function") {
throw new TypeError("type argument must be a string or function");
}
if (obj !== undefined && obj !== null && obj.constructor) {
//get the Function constructor
functionConstructor = obj.constructor;
while (functionConstructor != functionConstructor.constructor) {
functionConstructor = functionConstructor.constructor;
}
//get the object's window
context = functionConstructor == Function ? self : functionConstructor("return window")();
//get the constructor for the type
if (isTypeAString) {
//type is a string so we'll build the context (window.Array or window.some.Type)
for (typeArray = type.split("."), i = 0, l = typeArray.length; i < l && context; i++) {
context = context[typeArray[i]];
}
} else {
//type is a function so execute the function passing in the object's window
//the return should be a constructor
context = type(context);
}
//check if the object is an instance of the constructor
if (context) {
ret = obj instanceof context;
if (!ret && (type == "Number" || type == "String" || type == "Boolean")) {
ret = obj.constructor == context
}
}
}
return ret;
}
isInstance requires two parameters: an object and a type. The real trick to how it works is that it checks if the object is from the same window and if not gets the object's window.
Examples:
isInstance([], "Array"); //true
isInstance("some string", "String"); //true
isInstance(new Object(), "Object"); //true
function Animal() {}
function Dog() {}
Dog.prototype = new Animal();
isInstance(new Dog(), "Dog"); //true
isInstance(new Dog(), "Animal"); //true
isInstance(new Dog(), "Object"); //true
isInstance(new Animal(), "Dog"); //false
The type argument can also be a callback function which returns a constructor. The callback function will receive one parameter which is the window of the provided object.
Examples:
//"Arguments" type check
var args = (function() {
return arguments;
}());
isInstance(args, function(w) {
return w.Function("return arguments.constructor")();
}); //true
//"NodeList" type check
var nl = document.getElementsByTagName("*");
isInstance(nl, function(w) {
return w.document.getElementsByTagName("bs").constructor;
}); //true
One thing to keep in mind is that IE < 9 does not provide the constructor on all objects so the above test for NodeList would return false and also a isInstance(alert, "Function") would return false.
You can use the "instanceof" operator to determine if an object is an instance of a certain class or not. If you do not know the name of an object's type, you can use its constructor property. The constructor property of objects, is a reference to the function that is used to initialize them. Example:
function Circle (x,y,radius) {
this._x = x;
this._y = y;
this._radius = raduius;
}
var c1 = new Circle(10,20,5);
Now c1.constructor is a reference to the Circle() function.
You can alsow use the typeof operator, but the typeof operator shows limited information. One solution is to use the toString() method of the Object global object. For example if you have an object, say myObject, you can use the toString() method of the global Object to determine the type of the class of myObject. Use this:
Object.prototype.toString.apply(myObject);
You should use somevar.constructor.name like a:
_x000D_
const getVariableType = a => a.constructor.name.toLowerCase();_x000D_
_x000D_
const d = new Date();_x000D_
const res1 = getVariableType(d); // 'date'_x000D_
const num = 5;_x000D_
const res2 = getVariableType(num); // 'number'_x000D_
const fn = () => {};_x000D_
const res3 = getVariableType(fn); // 'function'_x000D_
_x000D_
console.log(res1); // 'date'_x000D_
console.log(res2); // 'number'_x000D_
console.log(res3); // 'function'You can use the instanceof operator to see if an object is an instance of another, but since there are no classes, you can't get a class name.
Source: Stackoverflow.com