Example

var sentence = document.createTextNode
  ("When you're smiling, the whole world smiles with you.");

sentence.deleteData(0, 21);

In the example above we create a Text node with the value When you're smiling, the whole world smiles with you., then we use the deleteData method to remove the first 22 characters (the characters between index 0 and 21 inclusive).

The final result is a single Text node with the data (and nodeValue) the whole world smiles with you., that has a length of 32.

If we then did this:

sentence.deleteData(15, 999);

The second argument is much larger than the total length of the string, so everything from character offset 15 to the end of the string will be deleted, and we'd end up with a Text node with the data (and nodeValue) the whole world, that has a length of 15.