const regex = new RegExp('(?=\\b\\d+[xX]\\b)', 'gm')
const str = `Some description art.nr: 4457 72 1x ACOUCH 90X200 NICE GRAY (3 colli) 1x matras 85x205x12 2x matras 80x190x11 Some specs 14x Premium otherproduct 90x200x23 HR34`;
const subst = `\n`;
// 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