JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="text1"></textarea>
<textarea id="text2"></textarea>
<br />
<button id="diff">test diff</button>

JavaScript

function testDiff(val1, val2){
    
    // textbox have more then 5 characters
  //  if();
    
    
    if(val1 == val2) return false;
    

    // split values to lines 
    var reg  = /\n/g;
    val1 = val1.split(reg);
    val2 = val2.split(reg);
    
    if(val1.length != val1.length) return true; // add or remove line(s)
    
    
    var line = 0,
        diffChar = 0;
    for( line in val1){
        if ( val1[line] == val2[line] ) continue; // to next line
        
        diffLength = val1[line].length - val2[line].length
        if(diffLength != 0){
            diffChar += Math.abs(diffLength);
        } else{
            for(var chr in val1[line]){
                if(val1[line][chr] != val2[line][chr]) diffChar++;
            }
        }
        
        if(diffChar > 4) return true;
        
    }
    return false; // change lass then 5 characters
    
}

$(document).ready(function(){
    $txt1 = $('#text1');
    $txt2 = $('#text2');
    
    $('#diff').click(function(){
        var val1   = $txt1.val(),
            val2   = $txt2.val();
        
        if(val2.length > 5){ // textbox2 have more then 5 characters
            var    isDiff = testDiff(val1, val2);
            alert(isDiff);
        }
    });
});