// str1 is the reference text.
    var str1 = "I was sent to earth to protect my cousin";

    // str2 is the text which I want to compare with str1.
    var str2 = "I was send to earth to protect my sister"

    function words(s) {
        return s.toLowerCase().match(/w+/g);
    }

    let a = words(str1);
    let b = words(str2);
    let res1 = b.filter(i => !a.includes(i));
    let res2 = a.filter(i => !b.includes(i));

    highlight(b, "str2", res1);
    function highlight(str, id, res){
        var text = "";
       for(var i=0; i<str.length; i++){
        var hasVal = res.includes(str[i]);
        if(hasVal){
          text +=" <span style='color:red'>"+str[i]+"</span> ";
        } else {
           text +=" "+str[i]+" ";
        }
       }
        document.write(text);
    }