JSFiddle - React, Tailwind, and code Playground

HTML

<div><input type="text" id="ipField">
  <button type="button" onclick="findGreatest()">Click</button></div>
<div id='repWord'></div>

JavaScript

function findGreatest() {

    var getString = document.getElementById('ipField').value.toLowerCase();
    var finalArray = [];
    var strArray = [];
    var tempArray = [];
    strArray = (getString.split(" "));
    // Take only those words which has repeated letter
    for (var i = 0, j = strArray.length; i < j; i++) {
        if ((/([a-zA-Z]).*?\1/).test(strArray[i])) {
            tempArray.push(strArray[i]);
        }
    }
    if (tempArray.length == 0) {       // If no word with repeated Character
        console.log('No such Word');
        return -1;
    } else {                 // If array has words with repeated character
        for (var x = 0, y = tempArray.length; x < y; x++) {
            var m = findRepWord(tempArray[x]);  // Find number of repeated character in it
            finalArray.push({
                name: tempArray[x], 
                repeat: m
            })
        }
      // Sort this array to get word with largest repeated chars
        finalArray.sort(function(z, a) {
            return a.repeat - z.repeat
        })
        document.getElementById('repWord').textContent=finalArray[0].name;
    }
}

// Function to find the word which as highest repeated character(s)
    function findRepWord(str) {
        try {
					return str.match(/(.)\1+/g).length;
        } catch (e) {
            return 0;
        } // if TypeError
    }