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create-gojs-kit

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A CLI for downloading GoJS samples, extensions, and docs

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url = url .slice(lindex + 1) .toLowerCase(); var aTags = navList.getElementsByTagName('a'); var currentindex = -1; for (var i = 0; i < aTags.length; i++) { var lowerhref = aTags[i] .href .toLowerCase(); if (lowerhref.indexOf('/' + url) !== -1) { currentindex = i; aTags[i] .classList .add('active'); break; } } } </script> <div class="px-4 pb-16 w-full overflow-hidden prose"> <h1>Collections</h1> <p> <b>GoJS</b> provides its own collection classes: <a>List</a>, <a>Set</a>, and <a>Map</a>. The latter two are very similar to the ECMAScript <b>Set</b> and <b>Map</b> classes, but iteration is quite different, using an <a>Iterator</a> instead of the ECMAScript <b>Iterator</b> protocol. </p> <p> These collection classes have several advantages over using JavaScript arrays as lists or objects as maps. They can be made read-only to avoid undesired modifications. If you are writing in TypeScript, they optionally enforce compile-time type checking of the item types. </p> <p> In <b>GoJS</b> most of the properties and methods that return collections describing the structure of the diagram return an <a>Iterator</a>. That is because the implementation of the collections are internal -- you only need to know how to iterate over the result collection. Other methods or properties will allow you to modify the diagram. An example is <a>Diagram.nodes</a>, which returns the current collection of <a>Node</a>s and <a>Group</a>s in the diagram as an <a>Iterator</a>. The collection is automatically modified as the programmer adds or removes node data in the model or by direct calls to <a>Diagram.add</a> or <a>Diagram.remove</a>. </p> <p> However there are a few properties that return collections that are allowed to be modified. Examples include collections on classes that are usually frozen after initialization: <a>Geometry.figures</a>, <a>PathFigure.segments</a>, and <a>Brush.colorStops</a>. Other examples include collections that are modified very infrequently, usually only upon diagram initialization: <a>ToolManager.mouseDownTools</a> (and the other lists of tools) and <a>Diagram.nodeTemplateMap</a> (and other template maps). </p> <p> See samples that make use of collections in the <a href="../samples/index.html#collections">samples index</a>. </p> <h2 id="List">List</h2> <p> A <a>List</a> is an ordered collection of values that are indexed by integers from zero to one less than the <a>List.count</a>. </p> <pre class="lang-js"><code> const l = new go.List(); l.add("A"); l.add("B"); l.add("C"); assert(l.count === 3); assert(l.elt(0) === "A"); assert(l.has("B")); assert(l.indexOf("B") === 1); l.setElt(1, "z"); // replace an item assert(l.elt(1) === "z"); l.removeAt(1); // remove an item assert(l.count === 2); assert(l.elt(1) === "C"); </code></pre> <p> However, if you are writing in TypeScript, GoJS collections classes (<code>List</code>, <code>Map</code>, <code>Set</code>) are now generic, and will help you enforce types: </p> <pre class="lang-ts"><code> // TypeScript: const l = new go.List&lt;string&gt;(); // Create a list of only strings l.add("A"); l.add(23); // produces an error during compilation or highlights it in an IDE l.add({}); // produces an error during compilation or highlights it in an IDE </code></pre> <p> To iterate over a <a>List</a>, get its <a>List.iterator</a> and call <a>Iterator.next</a> on it to advance its position in the list. Its <a>Iterator.value</a> will be a list item; its <a>Iterator.key</a> will be the corresponding index in the list. Or, more commonly, just call <a>List.each</a>. </p> <pre class="lang-js"><code> const l = new go.List(); l.add("A"); l.add("B"); l.add("C"); const it = l.iterator; while (it.next()) { console.log(it.key + ": " + it.value); } // This outputs: // 0: A // 1: B // 2: C // Or, if you just want to iterate over the items in the list: l.each(item => console.log(item)); </code></pre> <h2 id="Set">Set</h2> <p> A <a>Set</a> is an unordered collection of values that does not allow duplicate values. This class is similar to the <code>Set</code> object that is defined in ECMAScript 2015 (ES6). </p> <pre class="lang-js"><code> const s = new go.Set(); s.add("A"); s.add("B"); s.add("C"); s.add("B"); // duplicate is ignored assert(s.count === 3); assert(s.has("B")); s.delete("B"); // remove an item assert(s.count === 2); assert(!s.has("B")); </code></pre> <p> When writing TypeScript, it is a generic class so that the compiler can enforce types: </p> <pre class="lang-ts"><code> // TypeScript: const s = new go.Set&lt;string&gt;(); // Create a set of only strings s.add("A"); s.add(23); // produces an error during compilation or highlights it in an IDE s.add({}); // produces an error during compilation or highlights it in an IDE </code></pre> <p> Iterating over the items in a <a>Set</a> is just like iterating over a <a>List</a>, except that the order of the items may vary. </p> <pre class="lang-js"><code> const s = new go.Set(); s.add("A"); s.add("B"); s.add("C"); s.add("B"); // duplicate is ignored const it = s.iterator; while (it.next()) { console.log(it.value); } // This might output, perhaps in different order: // A // B // C // Or, equivalent code using Set.each: s.each(item => console.log(item)); </code></pre> <p> Furthermore, as of version 3, <a>Set</a> implements the ECMAScript <b>Iterable</b> protocol, by defining the <code>[Symbol.iterator]</code> property. This allows using the <code>for (let item of set) ...</code> statement. </p> <pre class="lang-js"><code> const s = new go.Set(); s.add("A"); s.add("B"); s.add("C"); // iteration using for ... of: for (let item of s) console.log(item); </code></pre> <p> Thus <a>Set</a>s can be used with spread syntax. For example: </p> <pre class="lang-js"><code> const s = new go.Set(); s.add("A"); s.add("B"); s.add("C"); const arr = [...set, "Z"]; // which is an Array of length 4: ["A", "B", "C", "Z"] </code></pre> <h2 id="Map">Map</h2> <p> A <a>Map</a> is an unordered collection of key-value pairs that are indexed by the keys. This class is similar to the <code>Map</code> object that is defined in ECMAScript 2015 (ES6). </p> <pre class="lang-js"><code> const m = new go.Map(); m.set("A", 1); // associate "A" with 1 m.set("B", 2); m.set("C", 3); assert(s.count === 3); assert(s.has("B")); assert(s.get("B") === 2); m.set("B", 222); // replace the value for "B" assert(s.get("B") === 222); s.delete("B"); // remove an item assert(s.count === 2); assert(!s.has("B")); assert(s.get("B") === null); </code></pre> <p> When writing TypeScript, it is a generic class so that the compiler can enforce types: </p> <pre class="lang-ts"><code> // TypeScript: const m = new go.Map&lt;string, number&gt;(); // Create a map of strings to numbers m.set("A", 1); m.set(23, 23); // produces an error during compilation or highlights it in an IDE m.set({}, 23); // produces an error during compilation or highlights it in an IDE </code></pre> <p> Iterating over the items in a <a>Map</a> is just like iterating over a <a>List</a>, but offering access to both the keys and the values. As with <a>Set</a>s the order of the items may vary. </p> <pre class="lang-js"><code> const m = new go.Map(); m.set("A", 1); // associate "A" with 1 m.set("B", 2); m.set("C", 3); m.set("B", 222); // replace the value for "B" // Normal iteration lets you get both the key and its corresponding value: const it = m.iterator; while (it.next()) { console.log(it.key + ": " + it.value); } // This might output, perhaps in different order: // A: 1 // B: 222 // C: 3 // Or, equivalently using Map.each: m.each(kvp => console.log(kvp.key + ": " + kvp.value)); // To get a collection of the keys, use Map.iteratorKeys: const kit = m.iteratorKeys; while (kit.next()) { console.log(kit.value); } // This might output, perhaps in different order: // A // B // C // To get a collection of the values, use Map.iteratorValues: const vit = m.iteratorValues; while (vit.next()) { console.log(vit.value); } // This might output, perhaps in different order: // 1 // 222 // 3 </code></pre> <p> Typically one uses <a>Map.iteratorKeys</a> or <a>Map.iteratorValues</a> when needing to pass a collection on to other methods that take an <a>Iterator</a>. </p> <p> As of version 3, <a>Map</a> implements the ECMAScript <b>Iterable</b> protocol, by defining the <code>[Symbol.iterator]</code> property. This allows using the <code>for (let item of map) ...</code> statement. </p> <pre class="lang-js"><code> const m = new go.Map(); m.add("A", 1); // associate "A" with 1 m.add("B", 2); m.add("C", 3); m.add("B", 222); // replace the value for "B" // ECMAScript iteration over the key and value pairs: for (let kvp of map) console.log(`${kvp[0]}: ${kvp[1]}`); // This might output, perhaps in different order: // A: 1 // B: 222 // C: 3 for (let k of map.iteratorKeys) console.log(k); // This might output, perhaps in different order: // A // B // C for (let v of map.iteratorValues) console.log(v); // This might output, perhaps in different order: // 1 // 222 // 3 </code></pre> <h2 id="MoreIterationExamples">More Iteration Examples</h2> <p> It is commonplace to iterate over the selected <a>Part</a>s of a <a>Diagram</a>: <pre class="lang-js"><code> for (let part of diagram.selection) { // part is now a Node or a Group or a Link or maybe a simple Part if (part instanceof go.Node) { . . . } else if (part instanceof go.Link) { . . . } } </code></pre> Alternatively: <pre class="lang-js"><code> diagram.selection.each(part => { // part is now a Node or a Group or a Link or maybe a simple Part if (part instanceof go.Node) { . . . } else if (part instanceof go.Link) { . . . } }); </code></pre> </p> <p> Sometimes one needs to iterate over the <a>Node</a>s in a <a>Diagram</a>: <pre class="lang-js"><code> for (let n of diagram.nodes) { // n is now a Node or a Group if (n.category === "Special") { . . . } } </code></pre> </p> <p> You can also iterate over the port elements in a <a>Node</a>, or the <a>Link</a>s connected to a port element: <pre class="lang-js"><code> for (let port of node.ports) { // port is now a GraphObject within the Node for (let link of node.findLinksConnected(port.portId)) { // link is now a Link connected with the port if (link.data.xyz === 17) { . . . } } } </code></pre> </p> <p> Or perhaps you need to iterate over the elements of a <a>Panel</a>: <pre class="lang-js"><code> for (let elt of panel.elements) { // elt is now a GraphObject that is an immediate child of the Panel if (elt instanceof go.TextBlock) { . . . } else if (elt instanceof go.Panel) { . . . recurse . . . } } </code></pre> </p> <p> If you want to find <a>Node</a>s that are immediate members of a <a>Group</a>: <pre class="lang-js"><code> for (let part of group.memberParts) { // part is now a Part within the Group if (part instanceof go.Node) { . . . maybe work with part.data . . . } } </code></pre> </p> </div> </div> <footer class="bg-white text-gray-900 border-t border-t-gray-200"> <div class="w-full max-w-screen-lg mx-auto px-4 py-6"> <p id="version" class="text-xs text-gray-900 m-0"></p> <div class="text-sm px-0 mb-4 grid grid-cols-2 sm:grid-cols-3 gap-y-10"> <div> <h2 class="text-base font-semibold text-nwoods-primary">GoJS</h2> <ul class="list-none space-y-4 md:space-y-1 px-0"> <li> <a href="../samples/index.html">Samples</a> </li> <li> <a href="../learn/index.html">Learn</a> </li> <li> <a href="../intro/index.html">Intro</a> </li> <li> <a href="../api/index.html">API</a> </li> <li> <a href="../changelog.html">Changelog</a> </li> <li> <a href="https://github.com/NorthwoodsSoftware/GoJS" target="_blank" rel="noopener">GitHub</a> </li> </ul> </div> <div> <h2 class="text-base font-semibold text-nwoods-primary">Support</h2> <ul class="list-none space-y-4 md:space-y-1 px-0"> <li> <a href="https://nwoods.com/contact.html" target="_blank" rel="noopener" onclick="getOutboundLink('https://nwoods.com/contact.html', 'contact');">Contact</a> </li> <li> <a href="https://forum.nwoods.com/c/gojs" target="_blank" rel="noopener">Forum</a> </li> <li> <a href="https://nwoods.com/app/activate.aspx?sku=gojs" target="_blank" rel="noopener">Activate</a> </li> <li> <a href="https://nwoods.com/sales/index.html" target="_blank" rel="noopener" onclick="getOutboundLink('https://nwoods.com/sales/index.html', 'buy');">Buy</a> </li> <li> <a href="https://nwoods.com/register.html" target="_blank" rel="noopener">Register</a> </li> </ul> </div> <div> <h2 class="text-base font-semibold text-nwoods-primary">Company</h2> <ul class="list-none space-y-4 md:space-y-1 px-0"> <li> <a target="_blank" href="https://nwoods.com" target="_blank" rel="noopener">Northwoods</a> </li> <li> <a target="_blank" href="https://nwoods.com/about.html" target="_blank" rel="noopener">About Us</a> </li> <li> <a target="_blank" href="https://nwoods.com/contact.html" target="_blank" rel="noopener">Contact Us</a> </li> <li> <a target="_blank" href="https://nwoods.com/consulting.html" target="_blank" rel="noopener">Consulting</a> </li> <li> <a target="_blank" href="https://twitter.com/northwoodsgo" target="_blank" rel="noopener">Twitter</a> </li> </ul> </div> </div> <p class="text-sm text-gray-900 md:mb-6"> Copyright 1998-2025 <a href="https://nwoods.com">Northwoods Software</a> </p> </div> </footer> </body> <script async src="https://www.googletagmanager.com/gtag/js?id=G-S5QK8VSK84"></script> <script> window.dataLayer = window.dataLayer || []; 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