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Test your skills: Form validation

This aim of this skill test is to assess whether you've understood our Client-side form validation article.

Note: You can try out solutions locally, however it may be helpful to put your code in an online tool such as CodePen, jsFiddle, or Glitch to work on the tasks.

If you get stuck, then ask us for help — see the Assessment or further help section at the bottom of this page.

Form validation 1

In this task, we are providing you with a simple support query form, and we want you to add some validation features to it:

  1. Make all of the input fields mandatory to complete before the form can be submitted.
  2. Change the type of the "Email address" and "Phone number" fields to make the browser apply some more specific validation suitable for the data being asked for.
  3. Give the "User name" field a required length of between 5 and 20 characters, the "Phone number" field a maximum length of 15 characters, and the "Comment" field a maximum length of 200 characters.

Try submitting your form — it should refuse to submit until the above constaints are followed, and give suitable error messages. To help, you might want to consider adding some simple CSS to show when a form field is valid or invalid.

Download the starting point for this task to work in your own editor or in an online editor.

Form validation 2

Now we want you to take the same form you saw in the previous task (use your previous answer if you want to), and add some more specific pattern validation to the first three fields using regular expressions.

  1. All of the user names in our application consist of a single letter, followed by a dot, followed by three or more letters or numbers. All letters should be lowercase.
  2. All of the email addresses for our users consist of one or more letters (lower or upper case) or numbers, followed by "@bigcorp.eu".
  3. Remove the length validation from the phone number field if it is present, and set it so that it accepts 10 digits — either 10 digits in a row, or a pattern of three digits, three digits, then four digits, separated by either spaces, dashes, or dots.

Note: Regular expressions are really challenging if you are new to them, but don't despair — have a go and see where you get to; there is no shame in asking for some help. You can find everything you need to answer these questions at our regular expression reference, and by searching on Stack Overflow.

Again, to help you might want to consider adding some simple CSS to show when a form field is valid or invalid.

Download the starting point for this task to work in your own editor or in an online editor.

Form validation 3

In our final task for this set, we are providing you with a similar example to what you saw in the accompanying article — a simple email address entry input. We would like you to use the constraint validation API, plus some form validation attributes, to program some custom error messages.

  1. Make the input mandatory to fill in, and give it a minimum length of 10 characters.
  2. Add an event listener that checks whether the inputted value is an email address, and whether it is long enough. If it doesn't look like an email address or is too short, provide the user with appropriate custom error messages.

Download the starting point for this task to work in your own editor or in an online editor.

Assessment or further help

You can practice these examples in the Interactive Editors above.

If you would like your work assessed, or are stuck and want to ask for help:

  1. Put your work into an online shareable editor such as CodePen, jsFiddle, or Glitch. You can write the code yourself, or use the starting point files linked to in the above sections.
  2. Write a post asking for assessment and/or help at the MDN Discourse forum Learning category. Your post should include:
    • A descriptive title such as "Assessment wanted for Form validation 1 skill test".
    • Details of what you have already tried, and what you would like us to do, e.g. if you are stuck and need help, or want an assessment.
    • A link to the example you want assessed or need help with, in an online shareable editor (as mentioned in step 1 above). This is a good practice to get into — it's very hard to help someone with a coding problem if you can't see their code.
    • A link to the actual task or assessment page, so we can find the question you want help with.

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Contributors to this page: chrisdavidmills
Last updated by: chrisdavidmills,