From 0ab9ec1ad327281f1452288a7de1c2ead21a1a8c Mon Sep 17 00:00:00 2001
From: Matt Lauber <github@mklauber.com>
Date: Wed, 9 May 2018 13:07:08 -0400
Subject: [PATCH] Refactored the is operator for simplicity and efficiency.
 (#3240)

* Refactored the is operator for simplicity and efficiency.

* Improve `is` filter documentation.

* Update is.js

* extracted `subops.length` to `num_of_subops`
* renamed `subop` to `operator` for clarity/differentiation from `subops`
* refactored to avoid using a `Set` object.

* Update is.js
---
 core/modules/filters/is.js               | 54 +++++++++++++-----------
 editions/tw5.com/tiddlers/filters/is.tid |  2 +-
 2 files changed, 30 insertions(+), 26 deletions(-)

diff --git a/core/modules/filters/is.js b/core/modules/filters/is.js
index 99d86597f..c1add6f61 100644
--- a/core/modules/filters/is.js
+++ b/core/modules/filters/is.js
@@ -27,40 +27,44 @@ Export our filter function
 */
 exports.is = function(source,operator,options) {
 
+	var isFilterOperators = getIsFilterOperators(),
+		subops = operator.operand.split("+"),
+		num_of_subops = subops.length;
 
-	if( !operator.operand) {
-		// Return all tiddlers if the operand is missing
+	//Make sure all the operands are defined.
+	for (var t = 0; t < num_of_subops; t++){
+		if( !isFilterOperators[subops[t]] ) {
+			return [$tw.language.getString("Error/IsFilterOperator")];
+		}
+	}
+
+	if(num_of_subops === 0) { 	// Return all tiddlers if the operand is missing
 		var results = [];
 		source(function(tiddler,title) {
 			results.push(title);
 		});
 		return results;
-	}
+	} else if(num_of_subops === 1) {	// Shortcut the Single Operator
+		var operator = isFilterOperators[subops[0]];
+		return operator(source,operator.prefix,options);
 
-	// Get our isfilteroperators
-	var isFilterOperators = getIsFilterOperators(),
-	    subops = operator.operand.split("+"),
-		filteredResults = {},
-		results = [];
-	for (var t=0; t<subops.length; t++) {
-		var subop = isFilterOperators[subops[t]];
-		if(subop) {
-			filteredResults[subops[t]] = subop(source,operator.prefix,options);
-		} else {
-			return [$tw.language.getString("Error/IsFilterOperator")];
+	} else {	// Handle multiple operators
+		var filtered_results = {},
+			results = [];
+		for(var t=0; t < num_of_subops; t++){
+			var operator = isFilterOperators[subops[t]];
+			operator(source,operator.prefix,options).forEach(function(element) { filtered_results[element] = "present"});
 		}
-		
+
+		// Sort the output by the input (There may be a better way to do this)
+		source(function(tiddler,title) {
+			if(filtered_results[title] === "present") {
+				results.push(title);
+			}
+		});
+
+		return results;
 	}
-	
-    source(function(tiddler,title) {
-        for (var t=0; t<subops.length; t++) {
-            if (filteredResults[subops[t]].indexOf(title) != -1){
-                results.push(title);
-                break;
-            }
-        }
-    });
-	return results;
 };
 
 })();
diff --git a/editions/tw5.com/tiddlers/filters/is.tid b/editions/tw5.com/tiddlers/filters/is.tid
index 214661839..51725e19d 100644
--- a/editions/tw5.com/tiddlers/filters/is.tid
+++ b/editions/tw5.com/tiddlers/filters/is.tid
@@ -14,7 +14,7 @@ op-neg-output: those input tiddlers that do <<.em not>> belong to category <<.pl
 The parameter <<.place C>> specifies zero or more fundamental categories using the following syntax:
 
 <$railroad text="""
-[{: ("current" | "missing" |: "orphans" | "shadows" | "tags" | "tiddlers" ) +"+" }]
+[{: ("current" | "missing" |: "orphan" | "shadow" | "system" | "tag" | "tiddler" | "image") +"+" }]
 """/>
 
 |!Category |!Matches any tiddler that... |