const regex = new RegExp('(AANVRAGER:)\\W*(.*?)\\W*(___LOCATIE)', 'gm')
const str = `[AANVRAAGNUMMER:__542-13___AANVRAGER: Dr.B.Leijnse en Dr.H.M. van Praag, ___LOCATIE:_Rotterdam___ONDERZOEKSONDERWERP: bestudering van het werkingsmechanisme van de anti-depressieve hydrazinen, in bio chemisch en psychiatrisch-psychologisch opzicht __BEDRAG:__ f 16.000] \\n`;
const subst = `\1\2\3`;
// 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