Question

I have strange error when I decided to build ordinary web-form validation with classic javascript. There are several “onblur” handlers for input text fields and one “form-submit” handler.

When I use them like that:

function loginCheck() {
  ... return true of false 
}

function passwordCheck() { 
   ...
}

function formValidation() {
  return loginCheck() && passwordCheck();
}

It doesn’t work as I expect: “passwordCheck” never called if loginCheck is failed!

Finally I have workaround

function formValidation() {
  ok = loginCheck();
  ok &= passwordCheck();
  return ok;
}

Now password check is executed. But when I choose:

function formValidation() {
      ok = loginCheck();
      ok = ok && passwordCheck();
      return ok;
    }

passwordCheck is never called again if loginCheck failed.

Moreover: loginCheck & passwordCheck return boolean values, but &= operator covert it to “0” or “1”. “0” doesn’t work for my onsubmit="return checkForm" handler. I have to convert my &= result to boolean once again:

function formValidation() {
      ok = loginCheck();
      ok &= passwordCheck();
      return ok != 0;
    }

It is a normal behavior for javascript engines ?

Answer 1

Yes, it’s normal. It’s called a short-circuit evaluation and is both handy and very common (i.e. is present in a lot of languages (C, C++, Java, Perl, many others), not just JavaScript).