replace use replacing en javascript code example

Example 1: how to replace all the string in javascript when the string is javascript variable

function name(str,replaceWhat,replaceTo){
    replaceWhat = replaceWhat.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
    var re = new RegExp(replaceWhat, 'g');
    return str.replace(re,replaceTo);
}

Example 2: javascript replace

var frase = "Son tres mil trescientos treinta y tres con nueve";
frase = frase.replace("tres","dos");
console.log(frase);
//Son dos mil trescientos treinta y tres con nueve