JSFiddle - React, Tailwind, and code Playground

by Kevin Van Lierde

HTML

<input id="test"/>

JavaScript

function addCommas(e) {
    var tgt = e.target, val = tgt.value.replace(/,/g, ''),
        amt = Math.ceil(val.length/3), newStr = '', x = 0; 
    while ( x <= amt ) {
        newStr += val.slice(x*3,(x+1)*3);
        newStr += ( x < amt-1 ) ? ',' : '';
        x++
    }
    tgt.value = newStr;
}
document.getElementById('test').addEventListener('change', addCommas, false);