Add fieldmangler widget that allows fields to be added and removed to tiddlers

core/modules/widgets/fieldmangler.js

@@ -0,0 +1,60 @@
+/*\
+title: $:/core/modules/widgets/fieldmangler.js
+type: application/javascript
+module-type: widget
+
+The fieldmangler widget modifies the fields of the current tiddler in response to messages.
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var FieldManglerWidget = function(renderer) {
+	// Save state
+	this.renderer = renderer;
+	// Generate child nodes
+	this.generate();
+};
+
+FieldManglerWidget.prototype.generate = function() {
+	var self = this;
+	// Get parameters from our attributes
+	this.tiddlerTitle = this.renderer.getAttribute("tiddler",this.renderer.tiddlerTitle);
+	// Set the element
+	this.tag = "div";
+	this.attributes = {
+		"class": "tw-fieldmangler"
+	};
+	// Set event handlers
+	this.events = [
+		{name: "tw-remove-field", handlerObject: this, handlerMethod: "handleRemoveFieldEvent"},
+		{name: "tw-add-field", handlerObject: this, handlerMethod: "handleAddFieldEvent"}
+	];
+	// Render the children
+	this.children = this.renderer.renderTree.createRenderers(this.renderer,this.renderer.parseTreeNode.children);
+};
+
+FieldManglerWidget.prototype.handleRemoveFieldEvent = function(event) {
+	var tiddler = this.renderer.renderTree.wiki.getTiddler(this.tiddlerTitle),
+		deletion = {};
+	deletion[event.currentField] = undefined;
+	this.renderer.renderTree.wiki.addTiddler(new $tw.Tiddler(tiddler,deletion));
+	return true;
+};
+
+FieldManglerWidget.prototype.handleAddFieldEvent = function(event) {
+	var tiddler = this.renderer.renderTree.wiki.getTiddler(this.tiddlerTitle);
+	if(typeof event.param === "string" && event.param !== "" && !$tw.utils.hop(tiddler.fields,event.param)) {
+		var addition = {};
+		addition[event.param] = "";
+		this.renderer.renderTree.wiki.addTiddler(new $tw.Tiddler(tiddler,addition));
+	}
+	return true;
+};
+
+exports.fieldmangler = FieldManglerWidget;
+
+})();