JSFiddle - React, Tailwind, and code Playground

JavaScript

var s = 'The cat in the hat';
var newStr = '';
var strArr = s.split(" ");
for (i=0;i<strArr.length;i++){
    alert(strArr[i]);

    if(strArr[i] == 'cat'){
        newStr  += ' <span>' + strArr[i] + '</span>';    
    }else{
            newStr  += ' ' + strArr[i];
    }       
}

alert(newStr);