Character Validation

• a for loop
• use of charAt() to extract characters from strings
• use of the focus() method to put the cursor into the field
• the break statement
• the onLoad and onChange events
• the this object
• the field is cleared when an "error" is detected
• the && comparison operator (logical AND)

JavaScript has the usual repertory of programming language statements, including:

• Conditionals: if, else, switch
• Loops: for, while, do while, break, continue
• Object Manipulation: for...in, new, this, with
• Comments: single-line (//) and multi-line (/*...*/)

Lab

Your task:

• Make a copy of the example form and modify it as follows.
• Change the instructions and the Javascript logic so that the text field accepts numbers only.
• You may find the || (logical OR) operator useful.

Solution

Don't peek unless you're stuck!

• Run it.
• Source code.