Javascript and PHP validation both working

I'm using both client and server side validation.When a user does not upload the file, but tries to click submit the js validation is printing the error but even then it is going to php code and validating.

When the user does not upload the file and js finds it, why is it executing php scripts?

If a user disable js,then PHP validation should work. Where am i doing wrong?

Why is it working like this?

Let me know if you want my code.

  function name()
      {
         x = true;
           checking the length
            if it does not satisfy showing error using span tag
           return false;
       }
    return x;
 

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