Check whether variable is number or string in JavaScript

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

typeof "Hello World"; // stringtypeof 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

Best way to do that is using isNaN + type casting:

Updated all-in method:

function isNumber(n) { return !isNaN(parseFloat(n)) && !isNaN(n - 0) }

The same using regex:

function isNumber(n) { return /^-?[\d.]+(?:e-?\d+)?$/.test(n); } ------------------------isNumber('123'); // true  isNumber('123abc'); // false  isNumber(5); // true  isNumber('q345'); // falseisNumber(null); // falseisNumber(undefined); // falseisNumber(false); // falseisNumber('   '); // false

The best way I have found is to either check for a method on the string, i.e.:

if (x.substring) {// do string thing} else{// do other thing}

or if you want to do something with the number check for a number property,

if (x.toFixed) {// do number thing} else {// do other thing}

This is sort of like "duck typing", it's up to you which way makes the most sense. I don't have enough karma to comment, but typeof fails for boxed strings and numbers, i.e.:

alert(typeof new String('Hello World'));alert(typeof new Number(5));

will alert "object".