# Editor example Client-side validation

Editor, in general, assumes that server-side validation of the data will be performed and any errors will be reported back to the client (the validation must be done at the server anyway for security, so this saves duplicating logic). However, there are cases where performing client-side checks can be very valuable, particularly if you want to avoid the overhead of making an Ajax request that contains known error information.

There are a number of methods for doing this with Editor, including simply not calling the `submit()` method when you don't want to submit the data, but this example shows how client-side validation can be achieved using the `preSubmit` event which can be used to cancel the submit by returning `false`.

The `preSubmit` event is used to run a custom function just before the data is submitted to the server. The `error()` method is used to show the error message to the end user, if required, and `inError()` to determine if the form shows an error state and thus not submit the form.

The validation performed here uses `field().isMultiValue()` to first determine if a field has multiple values or not - if it does, then no additional validation is performed since the end user can't have entered a value (when using the UI a multi-value edit effects all items being edited). If the user has entered a value (`field().val()`) it is checked to be not empty and <20 characters in length.

Note that the event handlers functions are executed in the Editor instance's scope, so API methods can be accessed using the `this` keyword.

Name | Position | Office | Extn. | Start date | Salary
--- | --- | --- | --- | --- | ---
Name | Position | Office | Extn. | Start date | Salary

- JavaScript
- HTML
- CSS
- Ajax
- Server-side script

The JavaScript shown below is used to initialise the table shown in this example:

`const editor = new DataTable.Editor({ ajax: '../php/staff.php', fields: [ { label: 'First name:', name: 'first_name' }, { label: 'Last name:', name: 'last_name' }, { label: 'Position:', name: 'position' }, { label: 'Office:', name: 'office' }, { label: 'Extension:', name: 'extn' }, { label: 'Start date:', name: 'start_date', type: 'datetime' }, { label: 'Salary:', name: 'salary' } ], table: '#example' }); editor.on('preSubmit', function (e, o, action) { if (action !== 'remove') { let firstName = this.field('first_name'); // Only validate user input values - different values indicate that // the end user has not entered a value if (!firstName.isMultiValue()) { if (!firstName.val()) { firstName.error('A first name must be given'); } if (firstName.val().length >= 20) { firstName.error( 'The first name length must be less that 20 characters' ); } } // ... additional validation rules // If any error was reported, cancel the submission so it can be corrected if (this.inError()) { return false; } } }); new DataTable('#example', { ajax: '../php/staff.php', columns: [ { data: null, render: (data) => data.first_name + ' ' + data.last_name }, { data: 'position' }, { data: 'office' }, { data: 'extn' }, { data: 'start_date' }, { data: 'salary', render: DataTable.render.number(null, null, 0, '$') } ], layout: { topStart: { buttons: [ { extend: 'create', editor: editor }, { extend: 'edit', editor: editor }, { extend: 'remove', editor: editor } ] } }, select: true });`

In addition to the above code, the following JavaScript library files are loaded for use in this example:

The HTML shown below is the raw HTML table element, before it has been enhanced by DataTables:

This example uses a little bit of additional CSS beyond what is loaded from the library files (below), in order to correctly display the table. The additional CSS used is shown below:

``

The following CSS library files are loaded for use in this example to provide the styling of the table:

This table loads data by Ajax. The latest data that has been loaded is shown below. This data will update automatically as any additional data is loaded.

The script used to perform the server-side processing for this table is shown below. Please note that this is just an example script using PHP. Server-side processing scripts can be written in any language, using the protocol described in the DataTables documentation.