use typeof();

example:

> typeof "foo""string"> typeof true"boolean"> typeof 42"number"

So you can do:

if(typeof bar === 'string') {//whatever}

Keep in mind that, typeof is only good for returning the "primitive" types, number, boolean, object, string. You can also use instanceof to test if an object is of a specific type.

function MyObj(prop) {this.prop = prop;}var obj = new MyObj(10);console.log(obj instanceof MyObj && obj instanceof Object); // outputs true

2021+ one liner answer.

My favourite way is not to use typeof

Why?because it doesn't give true type for other than boolean, string, number & function.

Then what?Here is small utility function using Object.prototype 🤩

var trueTypeOf = (obj) => Object.prototype.toString.call(obj).slice(8, -1).toLowerCase()

Results:

trueTypeOf([]); // arraytrueTypeOf({}); // objecttrueTypeOf(''); // stringtrueTypeOf(new Date()); // datetrueTypeOf(1); // numbertrueTypeOf(function () {}); // functiontrueTypeOf(/test/i); // regexptrueTypeOf(true); // booleantrueTypeOf(null); // nulltrueTypeOf(); // undefined

The best way is using typeof

typeof "blahha" 

I made a function with help of jQuery library code, jQuery library type method github link .

var getType = (function() {var objToString = ({}).toString ,typeMap = {},types = [ "Boolean", "Number", "String", "Function", "Array", "Date","RegExp", "Object", "Error"];for ( var i = 0; i < types.length ; i++ ){typeMap[ "[object " + types[i] + "]" ] = types[i].toLowerCase();}; return function( obj ){if ( obj == null ) {return String( obj );}// Support: Safari <= 5.1 (functionish RegExp)return typeof obj === "object" || typeof obj === "function" ?typeMap[ objToString.call(obj) ] || "object" :typeof obj;}}());

You can call it as getType("Hello")

typeof capitalized == 'string'

The getVarType method (below) works for almost all variables. Check out this fiddle. It first uses the very fast typeof for cases where the results are reliable. Then it uses a more expensive toString method for other cases. Finally, if it is dealing with a named object (as returned by Firefox for objects like document.location) it checks for Array-like objects and reports them as arrays.

In comparison, typeof is embarrassingly poor. typeof([]) returns 'object', typeof(new Number()) returns object. It also returns 'object' for many other variables that aren't (for practical purposes) objects. See the fiddle results for a comparison.

 // Begin public utility /getVarType/// Returns 'Function', 'Object', 'Array',// 'String', 'Number', 'Null', 'Boolean', or 'Undefined'//getVarType = (function () {var typeof_map = {'undefined' : 'Undefined','boolean' : 'Boolean','number' : 'Number','string' : 'String','function' : 'Function','Undefined' : 'Undefined','Null' : 'Null','Boolean' : 'Boolean','Number' : 'Number','String' : 'String','Function' : 'Function','Array' : 'Array','StyleSheetList' : 'Array'};return function( data ) {var type, type_str;if ( data === null ) { return 'Null'; }if ( data === undefined ) { return 'Undefined'; }type = typeof( data );type_str = typeof_map[ type ];if ( type_str ) { return type_str; }type = {}.toString.call( data ).slice( 8, -1 );return typeof_map[ type ]|| ( data instanceof Array ? 'Array' :( data.propertyIsEnumerable(0) && data.length !== undefined? 'Array' : 'Object' ));};}());// End public utility /getVarType/

The only possible failure mode happens if you are testing a named array that is empty (e.g. an empty enumerable DOM object besides the StyleSheetList). But on could add those to the type_of_map as needed.

I hope that helps!

ES-Next version with support BigInt & Symbol

"use strict";/**** @author xgqfrms* @license MIT* @copyright xgqfrms* @created 2020-06-09* @modified** @description js data type checker* @augments* @example* @link**/const dataTypeChecker = (data, debug = false) => {const log = console.log;let result = ``;const typeString = Object.prototype.toString.call(data);result = typeString.replace(/\[object /gi, ``).replace(/\]/gi, ``);if(debug) {log(`true type`, result)}return result;};/*export default dataTypeChecker;export {dataTypeChecker,};*/

test

const dataTypeChecker = (data, debug = false) => {const log = console.log;let result = ``;const typeString = Object.prototype.toString.call(data);// const typeString = Object.prototype.toString.apply(data);result = typeString.replace(/\[object /gi, ``).replace(/\]/gi, ``);if(!debug) {log(`true type`, result)}return result;};const obj = {};const func = () => {};dataTypeChecker(NaN)//"[object Number]"dataTypeChecker(undefined)//"[object Undefined]"dataTypeChecker(true)//"[object Boolean]"dataTypeChecker({})//"[object Object]"dataTypeChecker(func)//"[object Function]"dataTypeChecker(obj)//"[object Object]"dataTypeChecker(Symbol())//"[object Symbol]"dataTypeChecker(null)//"[object Null]"dataTypeChecker(123)//"[object Number]"dataTypeChecker(BigInt(1n))//"[object BigInt]"// true type Number// true type Undefined// true type Boolean// true type Object// true type Function// true type Object// true type Symbol// true type Null// true type Number// true type BigInt

 //-- difference constructor & typeof --//const fx = () => {}const arr = []const obj = {}console.log( fx.constructor == Function ) // trueconsole.log( arr.constructor == Array ) // trueconsole.log( arr.constructor == Object ) // falseconsole.log( obj.constructor == Object ) // trueconsole.log( obj.constructor == Array ) // falseconsole.log( typeof obj ) // objectconsole.log( typeof arr ) // object