Merge pull request #165 from Brennall/nextprev

Next and Previous filters plus tests and documentation

core/modules/filters/next.js

@@ -0,0 +1,43 @@
+/*\
+title: $:/core/modules/filters/next.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator returning the tiddler whose title occurs next in the list supplied in the operand tiddler
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.next = function(source,operator,options) {
+	var results = [],
+		list = options.wiki.getTiddlerList(operator.operand);
+
+	function checkTiddler(title) {
+		var match = list.indexOf(title);
+		// increment match and then test if result is in range
+		match++;
+		if(match > 0 && match < list.length) {
+			results.push(list[match]);
+		}
+	}
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		$tw.utils.each(source,function(title) {
+			checkTiddler(title);
+		});
+	} else {
+		$tw.utils.each(source,function(element,title) {
+			checkTiddler(title);
+		});
+	}
+	return results;
+};
+
+})();

core/modules/filters/previous.js

@@ -0,0 +1,43 @@
+/*\
+title: $:/core/modules/filters/previous.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator returning the tiddler whose title occurs immediately prior in the list supplied in the operand tiddler
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.previous = function(source,operator,options) {
+	var results = [],
+		list = options.wiki.getTiddlerList(operator.operand);
+
+	function checkTiddler(title) {
+		var match = list.indexOf(title);
+		// decrement match and then test if result is in range
+		match--;
+		if( match >= 0 ) {
+			results.push(list[match]);
+		}
+	}
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		$tw.utils.each(source,function(title) {
+			checkTiddler(title);
+		});
+	} else {
+		$tw.utils.each(source,function(element,title) {
+			checkTiddler(title);
+		});
+	}
+	return results;
+};
+
+})();

editions/test/tiddlers/tests/test-filters.js

@@ -148,6 +148,16 @@ describe("Filter tests", function() {
 		expect(wiki.filterTiddlers("[tag[one]list[TiddlerSeventh]sort[title]]").join(",")).toBe("Tiddler Three,TiddlerOne");
 	});
 
+  	it("should handle the next operator", function() {
+	    	expect(wiki.filterTiddlers("[[Tiddler Three]next[TiddlerSeventh]]").join(",")).toBe("a fourth tiddler");
+	    	expect(wiki.filterTiddlers("[[MissingTiddler]next[TiddlerSeventh]]").join(",")).toBe("");
+  	});
+
+  	it("should handle the previous operator", function() {
+    		expect(wiki.filterTiddlers("[[Tiddler Three]previous[TiddlerSeventh]]").join(",")).toBe("TiddlerOne");
+    		expect(wiki.filterTiddlers("[[TiddlerOne]previous[TiddlerSeventh]]").join(",")).toBe("");
+  	});
+
 	it("should handle the search operator", function() {
 		expect(wiki.filterTiddlers("[search[the]sort[title]]").join(",")).toBe("$:/TiddlerTwo,a fourth tiddler,one,Tiddler Three,TiddlerOne");
 		expect(wiki.filterTiddlers("[search{Tiddler8}sort[title]]").join(",")).toBe("$:/TiddlerTwo,a fourth tiddler,one,Tiddler Three,TiddlerOne");

editions/tw5.com/tiddlers/concepts/TiddlerFilters.tid

@@ -48,6 +48,8 @@ A filter string consists of one or more runs of filter operators that each look
 * ''links'': selects the outgoing links on the currently selected tiddlers
 * ''backlinks'': selects the tiddlers that link to the currently selected tiddlers
 * ''list'': selects the tiddlers listed in a specified [[TiddlerList|TiddlerLists]]
+* ''next'': selects the next item in a TiddlerList after the current tiddler
+* ''previous'': selects the previous item in a TiddlerList before the current tiddler
 * ''listed'': selects the TiddlerLists that include the current tiddler
 * ''each'': selects one tiddler for each discrete value of the specified field
 * ''eachday'': selects one tiddler for each discrete day in the specified date field