const regex = /(?<=\{\{[ _]*[Cc]ita[ _]+(?:web|libro|altro)(?:[^{}]|\{\{[^{}]*\}\})*)\s*\n\s*(?=\||\}\})/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('(?<=\\{\\{[ _]*[Cc]ita[ _]+(?:web|libro|altro)(?:[^{}]|\\{\\{[^{}]*\\}\\})*)\\s*\\n\\s*(?=\\||\\}\\})', 'gm')
const str = `{{cita libro | autore =Robert Sabatier
| titolo=Histoire de la poésie française
| volume=6
| tomo= 3
| editore=Albin Michel
| città =Parigi
| anno=1975
| pagina=313
}}`;
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