Check whether variable is number or string in JavaScript

Question

Does anyone know how can I check whether a variable is a number or a string in JavaScript?

Answer 1

If you're dealing with literal notation, and not constructors, you can use typeof:.

typeof "Hello World"; // string typeof 123;           // number 

If you're creating numbers and strings via a constructor, such as var foo = new String("foo"), you should keep in mind that typeof may return object for foo.

Perhaps a more foolproof method of checking the type would be to utilize the method found in underscore.js (annotated source can be found here),

var toString = Object.prototype.toString;  _.isString = function (obj) {   return toString.call(obj) == '[object String]'; } 

This returns a boolean true for the following:

_.isString("Jonathan"); // true _.isString(new String("Jonathan")); // true