javascript validation -

I am new to javascript and I want to validate three text boxes if I enter a value in the third lesson text box Click Submit and then, a warning box should be shown «Enter the first and second values.

Although it is easy, I do not know how to do it.

It is very easy when you submit, then check the value of each text box, only values ​​of 3 boxes Proceed with submitting with zero if not equal.

Actual Example:

  submit the process (if (document.getElementById ("inputbox1") .value == "") {warning ("error"); Return;} and if (document.getElementById ("input box 2"). Value == "") {warning ("error"); return;} and if (document.getElementById ("input box 3"). Value = = "") {Warning ("Error"); Return;} Else submitDetails (); // This is the function in which you actually use form.submit..etc}   < P> Just apply the above function. This is a difficult example. Individuals can use (such as white space, minimum and maximum length, etc.).