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

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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?

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?

• javascript
• string

Share Improve this question Follow edited Dec 26, 2017 at 11:26 Dov Miller 2,02855 gold badges3636 silver badges4848 bronze badges asked Dec 14, 2010 at 21:35 Vivian RiverVivian River 32.4k6464 gold badges210210 silver badges323323 bronze badges 4

• 2 The answer found here stackoverflow.com/questions/3192612 has the information on how to validate on alphanumeric. – JasCav Commented Dec 14, 2010 at 21:39
• 1 And to learn regular expressions: regular-expressions.info – Felix Kling Commented Dec 14, 2010 at 21:42
• For you jquery folks you should and could use inArray. – JonH Commented Apr 24, 2012 at 14:55
• 4 How input is formatted is not a human's problem. It's the computer's problem. Take whatever the user enters and remove all the characters that don't belong (non-alpha), test to see the result is 24 characters long, then validate it. User's really hate formatted input. – tggagne Commented Oct 19, 2013 at 16:15

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18 Answers 18

Sorted by: Reset to default 738

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:

http://www.regular-expressions.info/javascript.html

Alpha Numeric Regular Expression

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.

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;
    }
  };
}

You're all thinking too hard. Just use a simple Regular Expression, it's your best friend.

var string1 = "Hi Stack Overflow. I like to eat pizza."
var string2 = "Damn, I fail."

var regex = /(pizza)/g // Insert whatever phrase or character you want to find

string1.test(regex); // => true
string2.test(regex); // => false

Learn Regex in 5 minutes?

Use a regular expression to accomplish this.

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

If you're searching for character(s) in the start or at the end of the string, you can also use startsWith and endsWith

const country = "pakistan";
country.startsWith('p'); // true
country.endsWith('n');  // true

var inputString = "this is home";
var findme = "home";

if ( inputString.indexOf(findme) > -1 ) {
    alert( "found it" );
} else {
    alert( "not found" );
}

To test for alphanumeric characters only:

if (/^[0-9A-Za-z]+$/.test(yourString))
{
    //there are only alphanumeric characters
}
else
{
    //it contains other characters
}

The regex is testing for 1 or more (+) of the set of characters 0-9, A-Z, and a-z, starting with the beginning of input (^) and stopping with the end of input ($).

Kevins answer is correct but it requires a "magic" number as follows:

var containsChar = s.indexOf(somechar) !== -1;

In that case you need to know that -1 stands for not found. I think that a bit better version would be:

var containsChar = s.indexOf(somechar) >= 0;

Try this:

if ('Hello, World!'.indexOf('orl') !== -1)
    alert("The string 'Hello World' contains the substring 'orl'!");
else
    alert("The string 'Hello World' does not contain the substring 'orl'!");

Here is an example: http://jsfiddle.net/oliverni/cb8xw/

String's search function is useful too. It searches for a character as well as a sub_string in a given string.

'apple'.search('pl') returns 2

'apple'.search('x') return -1

If you are reading data from the DOM such as a p or h1 tag, for example, you will want to use two native JavaScript functions, it is quiet easy but limited to es6, at least for the solution I am going to provide. I will search all p tags within the DOM, if the text contains a "T" the entire paragraph will be removed. I hope this little example helps someone out!

HTML

<p>Text you need to read one</p>
<p>Text you need to read two</p>
<p>Text you need to read three</p>

JS

let paras = document.querySelectorAll('p');

paras.forEach(p => {
  if(p.textContent.includes('T')){
       p.remove();
    } 
});

Working perfectly.This exmple will help alot.

<script>    
    function check()
    {
       var val = frm1.uname.value;
       //alert(val);
       if (val.indexOf("@") > 0)
       {
          alert ("email");
          document.getElementById('isEmail1').value = true;
          //alert( document.getElementById('isEmail1').value);
       }else {
          alert("usernam");
          document.getElementById('isEmail1').value = false;
          //alert( document.getElementById('isEmail1').value);
       }
    }
</script>

<body>
    <h1>My form </h1>
    <form action="v1.0/user/login" method="post" id = "frm1">
        <p>
            UserName : <input type="text" id = "uname" name="username" />
        </p>
        <p>
            Password : <input type="text" name="password" />
        </p>
        <p>
            <input type="hidden" class="email" id = "isEmail1" name = "isEmail"/>
        </p>
        <input type="submit" id = "submit" value="Add User" onclick="return check();"/>
    </form>
</body>

A sample regex pattern test you can use to find out if the string contains a character '@':

/(@[A-Za-z])\w+/.test(str_text)

Check if string is alphanumeric or alphanumeric + some allowed chars

The fastest alphanumeric method is likely as mentioned at: Best way to alphanumeric check in Javascript as it operates on number ranges directly.

Then, to allow a few other extra chars sanely we can just put them in a Set for fast lookup.

I believe that this implementation will deal with surrogate pairs correctly correctly.

#!/usr/bin/env node

const assert = require('assert');

const char_is_alphanumeric = function(c) {
  let code = c.codePointAt(0);
  return (
    // 0-9
    (code > 47 && code < 58) ||
    // A-Z
    (code > 64 && code < 91) ||
    // a-z
    (code > 96 && code < 123)
  )
}

const is_alphanumeric = function (str) {
  for (let c of str) {
    if (!char_is_alphanumeric(c)) {
      return false;
    }
  }
  return true;
};

// Arbitrarily defined as alphanumeric or '-' or '_'.
const is_almost_alphanumeric = function (str) {
  for (let c of str) {
    if (
      !char_is_alphanumeric(c) &&
      !is_almost_alphanumeric.almost_chars.has(c)
    ) {
      return false;
    }
  }
  return true;
};
is_almost_alphanumeric.almost_chars = new Set(['-', '_']);

assert( is_alphanumeric('aB0'));
assert(!is_alphanumeric('aB0_-'));
assert(!is_alphanumeric('aB0_-*'));
assert(!is_alphanumeric('你好'));

assert( is_almost_alphanumeric('aB0'));
assert( is_almost_alphanumeric('aB0_-'));
assert(!is_almost_alphanumeric('aB0_-*'));
assert(!is_almost_alphanumeric('你好'));

GitHub upstream.

Tested in Node.js v10.15.1.

It's worked to me!

Attribute Contains Selector [name*=”value”]

This is the most generous of the jQuery attribute selectors that match against a value. It will select an element if the selector's string appears anywhere within the element's attribute value. Compare this selector with the Attribute Contains Word selector (e.g. [attr~="word"]), which is more appropriate in many cases.

source: Attribute Contains Selector [name*=”value”] => https://api.jquery.com/attribute-contains-selector/

 <!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>attributeContains demo</title>
  <script src="https://code.jquery.com/jquery-3.5.0.js"></script>
</head>
<body>
 
<input name="man-news">
<input name="milkman">
<input name="letterman2">
<input name="newmilk">
 
<script>
$( "input[name*='man']" ).val( "has man in it!" );
</script>
 
</body>
</html>

The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate.

const array1 = [1, 2, 3];

console.log(array1.includes(2));
// expected output: true

const pets = ['cat', 'dog', 'bat'];

console.log(pets.includes('cat'));
// expected output: true

console.log(pets.includes('at'));
// expected output: false

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