add comments for getHeaderWrapper() and getAllHeadersWrapper()

src/scriptlets/prevent-xhr.js

@@ -222,6 +222,15 @@ export function preventXHR(source, propsToMatch, customResponseText) {
         return undefined;
     };
 
+    /**
+     * Mock XMLHttpRequest.prototype.getHeaderHandler() to avoid adblocker detection.
+     *
+     * @param {Function} target XMLHttpRequest.prototype.getHeaderHandler().
+     * @param {XMLHttpRequest} thisArg The request.
+     * @param {string[]} args Header name is passed as first argument.
+     *
+     * @returns {string|null} Header value or null if header is not set.
+     */
     const getHeaderWrapper = (target, thisArg, args) => {
         if (!thisArg.collectedHeaders.length) {
             return null;
@@ -238,6 +247,14 @@ export function preventXHR(source, propsToMatch, customResponseText) {
             : null;
     };
 
+    /**
+     * Mock XMLHttpRequest.prototype.getAllResponseHeaders() to avoid adblocker detection.
+     *
+     * @param {Function} target XMLHttpRequest.prototype.getAllResponseHeaders().
+     * @param {XMLHttpRequest} thisArg The request.
+     *
+     * @returns {string} All headers as a string. For no headers an empty string is returned.
+     */
     const getAllHeadersWrapper = (target, thisArg) => {
         if (!thisArg.collectedHeaders.length) {
             return '';