deleting a line in a string

HTML

<textarea id="input">This is text that contains some string bla This is text that contains
some string bla This is text DELETEME some string bla This is text
that contains some string bla This is text that contains some string
    bla</textarea>

<textarea id="output"></textarea>

CSS

textarea { width: 100%; height:100px }

JavaScript

string = document.getElementById('input').value;

string = string.replace(/.*DELETEME.*/, "XXXX");

document.getElementById('output').value = string;