const regex = /(?<=id:\s*'[^']*?)\s(?=[^']*')/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('(?<=id:\\s*\'[^\']*?)\\s(?=[^\']*\')', 'gm')
const str = `var user1 = {id: 'Alan Banks'};
var user2 = {id: 'Chris Daily'};
var user1 = {id: 'Alan Banks TEXT here'};
var user2 = {id: 'Chris Daily More text'};`;
const subst = `_`;
// 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