View source for Joomla 4 Tips and Tricks: Form Validation Basics

=== Numeric ===

<source lang="javascript">
this.setHandler('numeric', value => {
      const regex = /^(\d|-)?(\d|,)*\.?\d*$/;
      return regex.test(value);
    });</source>
Here the value must start with a digit or minus sign zero or one times, be followed by a digit or a comma zero or more times, followed by a full stop zero or one times, ending with a digit zero or more times. So this will match 3.142 or -10 or 100,000.0 and so on. The actual number needs to match whatever the field type is in the database. The expression will not match numbers with exponents, so 10e2 will be rejected.