const regex = /(?<![\.\n]) ?\n(?!\n)/gsm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('(?<![\\.\\n]) ?\\n(?!\\n)', 'gsm')
const str = `Below, we present an
introduction to advanced.
regular expressions, with eight commonly used concepts and examples.
Each example outlines a simple way to match patterns in complex strings.
If you do not yet have experience with basic regular expressions, have a look at this article to get started. The syntax used here matches PHP regular expressions.Regular expressions (or regex) are a powerful way to traverse large strings in order to find information. They rely on underlying patterns in a string’s structure to work their magic. Unfortunately, simple regular expressions are unable to cope with complex patterns and symbols. To deal with this dilemma, you can use advanced regular expressions.`;
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