const regex = /^.*?\+?0*610?(\d{3})(\d{3})(\d{4})(?!\d).*$/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('^.*?\\+?0*610?(\\d{3})(\\d{3})(\\d{4})(?!\\d).*$', 'gm')
const str = `xgsh6101231231234vvajxxgsh6101231231234vvajx
xgsh06101231231234vvajx
xgsh000006101231231234vvajx
+6101231231234
xgsh61012312312345vvajx
xgsh5101231231234vvajx
xgsh00000101231231234vvajx
xgsh6143545626455345601231231234vvajx
`;
const subst = `+61 (0) $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