Question

I’ve got a function which validate the length of the value of a field,

function validateName(name) {
  if(name.val().length < 5) {
  }
}

I want to check also for the presence of white spaces.
I tried with this but it didn’t work:

function validateName(name) {
  if(name.val().length < 5 && name.val(" ") < 0) {
  }
}

Answer 1

The problem in the code above is that $.fn.val changes behaviour on the basis of the arguments it receives as input; and specifically, it’s a getter when it’s executed without parameters, and a setter when it’s executed with one parameter.
So this line:

name.val(" ")

doesn’t check for the presence of empty space in the value, but set the value to a single empty space.

There’re numerous different approaches to check if a string contains at least an empty space; here I’ll go for String#indexOf, so that the validateName function can be written as:

function validateName(name) {
  var val = name.val();
  if (val && val.length < 5 && val.indexOf(" ") < 0) {
    // valid!
  }
}

A more expressive approach would be to use String#includes, but it’s also less widely supported by browsers.

function validateName(name) {
  var val = name.val();
  if (val && val.length < 5 && val.indexOf(" ") < 0) {
    console.log("valid", val);
  } else {
    console.log("invalid", val);
  }
}

validateName($('<input value="b" />'));
validateName($('<input value="br" />'));
validateName($('<input value="bru" />'));
validateName($('<input value="brun" />'));
validateName($('<input value="bruno" />'));
validateName($('<input value="b ru" />'));
validateName($('<input />'));

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

Also, as general advice I wouldn’t mess the validation logic with jQuery; that is, it would be better for validateName to accept as input a plain string, not a jQuery object representing the input field.