Error alert problem

[MSK7]

Hi to all,
Can you please suggest me, How a Javascript validation can be applied in my form so that a when a user enters wrong data in the form, a Error message should alert at a time of mistake,

" Before (click on submit button or) submitting the form " ?

(1) "Invalid" or "Numeric value" should Not be entered in the textbox of "Name" field .

(2) when a user enters more than two digits in the textbox of "Age" field,
at a time a message should alert for Not to enter more than two digit values.

(3) when a user enters more or less than 10 digits for his mobile number, an
Error messsage should alert at a time that you entered more or less than 10 digit numbers in the textbox of "Mobile" field. please enter only 10 digit number.

please suggest me javascript validation for throwing Error message alert
at a time of mistake , before submitting the form.

In advance ,

Thanks & Regards.

[Krik]

Use "onblur" in the <input> tag to trigger a function that will check that field and then generate an alert() if needed.