Improve logging capabilities of json-prune scriptlet

Specifically:

- Log entries as received by client code
- Prettier and more readable console output
- Ability to only log entries matching a
  specific needle

As per internal discussion at
<https://github.com/uBlockOrigin/uAssets>; limited
logging capabilities of json-prune originally raised
by <https://github.com/gwarser>.

assets/resources/resources.txt

@@ -1374,15 +1374,30 @@ addEventListener-logger.js application/javascript
 # https://github.com/gorhill/uBlock/commit/2fd86a66fcc2665e5672cc5862e24b3782ee7504
 json-prune.js application/javascript
 (function() {
-	const log = console.log.bind(console);
 	const rawPrunePaths = '{{1}}';
 	const rawNeedlePaths = '{{2}}';
 	const prunePaths = rawPrunePaths !== '{{1}}' && rawPrunePaths !== ''
 		? rawPrunePaths.split(/ +/)
 		: [];
-	const needlePaths = rawNeedlePaths !== '{{2}}' && rawNeedlePaths !== ''
-		? rawNeedlePaths.split(/ +/)
-		: [];
+	let needlePaths;
+	let log, reLogNeedle;
+	if ( prunePaths.length !== 0 ) {
+		needlePaths = prunePaths.length !== 0 &&
+					  rawNeedlePaths !== '{{2}}' && rawNeedlePaths !== ''
+			? rawNeedlePaths.split(/ +/)
+			: [];
+	} else {
+		log = console.log.bind(console);
+		let needle;
+		if ( rawNeedlePaths === '' || rawNeedlePaths === '{{2}}' ) {
+			needle = '.?';
+		} else if ( rawNeedlePaths.charAt(0) === '/' && rawNeedlePaths.slice(-1) === '/' ) {
+			needle = rawNeedlePaths.slice(1, -1);
+		} else {
+			needle = rawNeedlePaths.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+		}
+		reLogNeedle = new RegExp(needle);
+	}
 	const findOwner = function(root, path) {
 		let owner = root;
 		let chain = path;
@@ -1410,8 +1425,11 @@ json-prune.js application/javascript
 	JSON.parse = new Proxy(JSON.parse, {
 		apply: function() {
 			const r = Reflect.apply(...arguments);
-			if ( prunePaths.length === 0 ) {
-				log(location.hostname, r);
+			if ( log !== undefined ) {
+				const json = JSON.stringify(r, null, 2);
+				if ( reLogNeedle.test(json) ) {
+					log(location.hostname, json);
+				}
 				return r;
 			}
 			if ( mustProcess(r) === false ) { return r; }