Question

I have a single form field and I need to be able to detect when the field changes and execute some additional code using the new value of the field. I only want to execute the code if the key pushed actually changes the value of the text box. Here’s the solution I came up with.

function onkeypress(e) {
  var value = this.value;
  // do something with 
}

function onkeyup(e) {
  if ( e.which == 8 || e.keyCode == 46 ) { // delete or backspace keys
    this.onkeypress(e);
  }
}

There’s just one problem though. onkeypress is fired before the field’s value is updated, so when I grab the value, I’m getting the previous value. I would use keyup exclusively if I knew a way to test whether the key changed the value or not, but some characters (like the arrow keys) have no effect on the field’s value.

Any ideas?

Answer 1

The way I do this is simply with a variable along the lines of prevValue. At the end of the key press function, store the value in that variable, and only execute the function again if the value doesn’t equal that previous value.