const regex = /(?=^\d,\d\d$)|(?<=^\d\d,\d$)|(?<=^\d,\d$)|(?=^\d,\d$)/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('(?=^\\d,\\d\\d$)|(?<=^\\d\\d,\\d$)|(?<=^\\d,\\d$)|(?=^\\d,\\d$)', 'gm')
const str = `1,12
1,1
11,1`;
const subst = `0`;
// 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