const p = 'dog dog cat rat';
const regex = /dog/gi;
console.log(p.replace(regex, 'cow'));
//if pattern is regular expression all matches will be replaced
//output: "cow cow cat rat"
function name(str,replaceWhat,replaceTo){
replaceWhat = replaceWhat.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
var re = new RegExp(replaceWhat, 'g');
return str.replace(re,replaceTo);
}