How to change Label Value using javascript

very simple

$('#label-ID').text("label value which you want to set");

This will work in Chrome

// get your input
var input = document.getElementById('txt206451');
// get it's (first) label
var label = input.labels[0];
// change it's content
label.textContent = 'thanks'

But after looking, labels doesn't seem to be widely supported..

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You can use querySelector

// get txt206451's (first) label
var label = document.querySelector('label[for="txt206451"]');
// change it's content
label.textContent = 'thanks'