How to tell if a string contains a certain character in JavaScript?


I have a page with a textbox where a user is supposed to enter a 24 character (letters and numbers, case insensitive) registration code. I used maxlength to limit the user to entering 24 characters.

The registration codes are typically given as groups of characters separated by dashes, but I would like for the user to enter the codes without the dashes.

How can I write my JavaScript code without jQuery to check that a given string that the user inputs does not contain dashes, or better yet, only contains alphanumeric characters?

12/26/2017 11:26:56 AM

Accepted Answer

To find "hello" in your_string

if (your_string.indexOf('hello') > -1)
  alert("hello found inside your_string");

For the alpha numeric you can use a regular expression:

Alpha Numeric Regular Expression

5/23/2017 11:47:27 AM

With ES6 MDN docs .includes()

"FooBar".includes("oo"); // true

"FooBar".includes("foo"); // false

"FooBar".includes("oo", 2); // false

E: Not suported by IE - instead you can use the Tilde opperator ~ (Bitwise NOT) with .indexOf()

~"FooBar".indexOf("oo"); // -2 -> true

~"FooBar".indexOf("foo"); // 0 -> false

~"FooBar".indexOf("oo", 2); // 0 -> false

Used with a number, the Tilde operator effective does ~N => -(N+1). Use it with double negation !! (Logical NOT) to convert the numbers in bools:

!!~"FooBar".indexOf("oo"); // true

!!~"FooBar".indexOf("foo"); // false

!!~"FooBar".indexOf("oo", 2); // false


If you have the text in variable foo:

if (! /^[a-zA-Z0-9]+$/.test(foo)) {
    // Validation failed

This will test and make sure the user has entered at least one character, and has entered only alphanumeric characters.


check if string(word/sentence...) contains specific word/character

if ( "write something here".indexOf("write som") > -1 )  { alert( "found it" );  } 

ES6 contains inbuilt method (includes) in String's prototype, which can be used to check if string contains another string or not.

var str = 'To be, or not to be, that is the question.';

console.log(str.includes('To be')); 

Following polyfill can be used to add this method in non-supported browsers. (Source)

if (!String.prototype.includes) {
  String.prototype.includes = function(search, start) {
    'use strict';
    if (typeof start !== 'number') {
      start = 0;
    if (start + search.length > this.length) {
      return false;
    } else {
      return this.indexOf(search, start) !== -1;


Use a regular expression to accomplish this.

function isAlphanumeric( str ) {
 return /^[0-9a-zA-Z]+$/.test(str);

Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Email: [email protected]