const regex = /((?:\d{2})(?:\:\d{2}){2}).*?\[\s(\d+).*?\[\s(\d+)/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('((?:\\d{2})(?:\\:\\d{2}){2}).*?\\[\\s(\\d+).*?\\[\\s(\\d+)', 'gm')
const str = `Line 394 : [21:44:07 Oct 12 Fri] @0x3924004E|JVM| Free Memory: Heap [ 2368340/ 6291456], Native[ 7299824/32505856]`;
const subst = `\1,\2,\3`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions