I want a pattern with letters and numbers only.

This is how I do it...

JavaScript file:

var pattern_checked = checkPattern(); 

function checkPattern(){
        var elem = document.getElementById("name");

        var pattern = elem.getAttribute("[a-zA-Z0-9_]");
        var re = new RegExp(pattern);
        if (re.test(elem.value)) {
            return true;
        } else {
            return false;
        }
    }

But in both the cases, I'm getting false.

What is wrong in this code?

I want a pattern with letters and numbers only.

This is how I do it...

JavaScript file:

var pattern_checked = checkPattern(); 

function checkPattern(){
        var elem = document.getElementById("name");

        var pattern = elem.getAttribute("[a-zA-Z0-9_]");
        var re = new RegExp(pattern);
        if (re.test(elem.value)) {
            return true;
        } else {
            return false;
        }
    }

But in both the cases, I'm getting false.

What is wrong in this code?

• javascript
• regex
• pattern-matching

• Can you post your html also .Are you sure you have attribute like [a-zA-Z0-9_] this in your html .i think its a pattern attr – prasanth Commented May 30, 2017 at 7:36
• 2 Did you check what elem.getAttribute("[a-zA-Z0-9_]") will return??? – Tushar Commented May 30, 2017 at 7:37
• I guess your pattern is the attributes value. elem.getAttribute("attributeName") would return your pattern. – Eytibi Commented May 30, 2017 at 7:42
• @prasad I think I'm doing something wrong. How do I use that pattern? – ishan shah Commented May 30, 2017 at 7:42
• 1 yes you are doing wrong .That why i was asking the html code @ishanshah – prasanth Commented May 30, 2017 at 7:43

3 Answers 3

I believe you meant to do:

function checkPattern() {
    var elem = document.getElementById("name");

    // Allow A-Z, a-z, 0-9 and underscore. Min 1 char.
    var re = /^[a-zA-Z0-9_]+$/;

    return re.test(elem.value);
}

Example fiddle

Your problem should be at this line.

var pattern = elem.getAttribute("[a-zA-Z0-9_]");

Attribute should usually have a name with value. But from your example, it seems like the value is also name. The HTML code should be something like below:-

<input type='text' id='name' pattern='[a-zA-Z0-9_]'>

Then to get the pattern

var pattern = elem.getAttribute("pattern");

With pure jquery/js it is possible:

<input type="text" placeholder="Ex 15.04.2023" class="date" required pattern="\d\d\.\d\d\.\d{4}"/>


css:
.date:invalid{
    background:red !important;
}

script:
$('.date').keyup(function(){
  console.log($('.date:valid').length)
});