const regex = /[A-Za-z0-9 ']*(?:(?:~~|&&)[A-Za-z0-9 ']*)*\K(?:[^A-Za-z0-9 ']|\z)/g;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('[A-Za-z0-9 \']*(?:(?:~~|&&)[A-Za-z0-9 \']*)*\\K(?:[^A-Za-z0-9 \']|\\z)', 'g')
const str = `I like~~cake~too&&m~~~~u~~~~~ch&now.~~~gh
a~&a`;
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