create-gojs-kit
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A CLI for downloading GoJS samples, extensions, and docs
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<meta name="description" content="This variation on the LinkLabelDraggingTool extension restricts link labels to stay on the link's route while the user is dragging it." />
<meta itemprop="description" content="This variation on the LinkLabelDraggingTool extension restricts link labels to stay on the link's route while the user is dragging it." />
<meta property="og:description" content="This variation on the LinkLabelDraggingTool extension restricts link labels to stay on the link's route while the user is dragging it." />
<meta name="twitter:description" content="This variation on the LinkLabelDraggingTool extension restricts link labels to stay on the link's route while the user is dragging it." />
<link rel="preconnect" href="https://rsms.me/">
<link rel="stylesheet" href="../assets/css/style.css">
<!-- Copyright 1998-2025 by Northwoods Software Corporation. -->
<meta itemprop="name" content="Dragging Link Label along Path" />
<meta property="og:title" content="Dragging Link Label along Path" />
<meta name="twitter:title" content="Dragging Link Label along Path" />
<meta property="og:image" content="https://gojs.net/latest/assets/images/screenshots/linklabelonpathdragging.png" />
<meta itemprop="image" content="https://gojs.net/latest/assets/images/screenshots/linklabelonpathdragging.png" />
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<title>
Dragging Link Label along Path | GoJS Diagramming Library
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<div class="flex flex-col prose">
<div class="w-full max-w-screen-xl mx-auto">
<!-- * * * * * * * * * * * * * -->
<!-- Start of GoJS sample code -->
<script src="https://cdn.jsdelivr.net/npm/gojs@3.1.0"></script>
<div id="allSampleContent" class="p-4 w-full">
<script src="../extensions/LinkLabelOnPathDraggingTool.js"></script>
<script id="code">
function init() {
myDiagram = new go.Diagram('myDiagramDiv', {
layout: new go.ForceDirectedLayout({ defaultSpringLength: 50, defaultElectricalCharge: 50 }),
'undoManager.isEnabled': true
});
// install the LinkLabelDraggingTool as a "mouse move" tool
myDiagram.toolManager.mouseMoveTools.insertAt(0, new LinkLabelOnPathDraggingTool());
myDiagram.nodeTemplate =
new go.Node('Auto', { locationSpot: go.Spot.Center })
.add(
new go.Shape({
fill: 'orange', // default fill color
portId: '',
fromLinkable: true,
fromSpot: go.Spot.AllSides,
toLinkable: true,
toSpot: go.Spot.AllSides,
cursor: 'pointer'
})
.bind('fill', 'color'),
new go.TextBlock({ margin: 10, font: 'bold 12pt sans-serif' })
.bind('text')
);
myDiagram.linkTemplate =
new go.Link({
routing: go.Routing.AvoidsNodes,
corner: 5,
relinkableFrom: true,
relinkableTo: true,
reshapable: true,
resegmentable: true
})
.add(
new go.Shape(),
new go.Shape({ toArrow: 'OpenTriangle' }),
new go.Panel('Auto', {
// mark this Panel as being a draggable label, and set default segment props
segmentIndex: NaN, segmentFraction: 0.5
})
.attach({ // GraphObject.attach() is used to set non-predefined properties
_isLinkLabel: true
})
// remember any modified segment properties in the link data object
.bindTwoWay('segmentFraction')
.add(
new go.Shape({ fill: 'white' }),
new go.TextBlock('?', { margin: 3 })
.bind('text', 'color')
)
);
// create a few nodes and links
myDiagram.model = new go.GraphLinksModel(
[
{ key: 1, text: 'one', color: 'lightyellow' },
{ key: 2, text: 'two', color: 'brown' },
{ key: 3, text: 'three', color: 'green' },
{ key: 4, text: 'four', color: 'slateblue' },
{ key: 5, text: 'five', color: 'aquamarine' },
{ key: 6, text: 'six', color: 'lightgreen' },
{ key: 7, text: 'seven' }
],
[
{ from: 5, to: 6, color: 'orange' },
{ from: 1, to: 2, color: 'red' },
{ from: 1, to: 3, color: 'blue' },
{ from: 1, to: 4, color: 'goldenrod' },
{ from: 2, to: 5, color: 'fuchsia' },
{ from: 3, to: 5, color: 'green' },
{ from: 4, to: 5, color: 'black' },
{ from: 6, to: 7 }
]
);
}
window.addEventListener('DOMContentLoaded', init);
</script>
<div id="sample">
<div id="myDiagramDiv" style="background-color: whitesmoke; border: solid 1px black; width: 100%; height: 600px"></div>
<p>
This sample demonstrates a custom Tool, LinkLabelOnPathDraggingTool, that allows the user to drag the label of a Link, but that keeps the label exactly on
the path of the link. The tool is defined at <a href="../extensions/LinkLabelOnPathDraggingTool.js">LinkLabelOnPathDraggingTool.js</a>.
</p>
<p>
The label on the link can be any arbitrarily complex object. It is positioned by the <a>GraphObject.segmentIndex</a> and
<a>GraphObject.segmentFraction</a> properties. The segmentIndex is set to NaN such that the whole link path acts as the segment, and the segmentFraction is
set by the LinkLabelOnPathDraggingTool. A two-way data binding on segmentFraction automatically remembers any modified value on the link data object in the
model.
</p>
<p>
The tool is derived from a similar tool, <a href="../extensions/LinkLabelDraggingTool.js">LinkLabelDraggingTool.js</a>, that allows the user to drag the label in any
direction from the mid-point of the Link path.
</p>
</div>
</div>
<!-- * * * * * * * * * * * * * -->
<!-- End of GoJS sample code -->
</div>
<div id="allTagDescriptions" class="p-4 w-full max-w-screen-xl mx-auto">
<hr/>
<h3 class="text-xl">GoJS Features in this sample</h3>
<!-- blacklist tags that do not correspond to a specific GoJS feature -->
<h4>Tools</h4>
<p>
<a href="../api/symbols/Tool.html" target="api">Tool</a>s handle all input events, such as mouse and keyboard interactions, in a Diagram.
There are many kinds of predefined Tool classes that implement all of the common operations that users do.
</p>
<p>
For flexibility and simplicity, all input events are canonicalized as <a href="../api/symbols/InputEvent.html" target="api">InputEvent</a>s and
redirected by the diagram to go to the <a href="../api/symbols/Diagram.html#currentTool" target="api">Diagram.currentTool</a>.
By default the Diagram.currentTool is an instance of <a href="../api/symbols/ToolManager.html" target="api">ToolManager</a> held as the <a href="../api/symbols/Diagram.html#toolManager" target="api">Diagram.toolManager</a>.
The ToolManager implements support for all mode-less tools.
The ToolManager is responsible for finding another tool that is ready to run and then making it the new current tool.
This causes the new tool to process all of the input events (mouse, keyboard, and touch) until the tool decides that it is finished,
at which time the diagram's current tool reverts back to the <a href="../api/symbols/Diagram.html#defaultTool" target="api">Diagram.defaultTool</a>, which is normally the ToolManager, again.
</p>
<p>
More information can be found in the <a href="../intro/tools.html">GoJS Intro</a>.
</p>
<p>
<a href="../samples/index.html#tools">Related samples</a>
</p>
<hr>
<!-- blacklist tags that do not correspond to a specific GoJS feature -->
<h4>GoJS Extensions</h4>
<p>
<b>GoJS</b> can be extended in a variety of ways.
The most common way to change the standard behavior is to set properties on the <a href="../api/symbols/GraphObject.html" target="api">GraphObject</a>, <a href="../api/symbols/Diagram.html" target="api">Diagram</a>, <a href="../api/symbols/CommandHandler.html" target="api">CommandHandler</a>, <a href="../api/symbols/Tool.html" target="api">Tool</a>, or <a href="../api/symbols/Layout.html" target="api">Layout</a>.
But when the desired property does not exist, you might need to override methods of CommandHandler, Tool, Layout, Link, or Node.
Methods that you can override are documented in the API reference.
Various features of GoJS can be overriden, either by replacing a method on an instance (a feature of JavaScript) or by defining a subclass.
You should not modify the prototypes of any of the <b>GoJS</b> classes.
</p>
<p>
In addition to our samples, <b>GoJS</b> provides an <strong><a href="../samples/#extensions">extensions gallery</a></strong>,
showcasing the creation of custom tools and layouts.
Those classes and samples are written in TypeScript, available at <code>../extensionsJSM/</code>,
as ECMAScript/JavaScript modules -- these use the <code>../release/go-module.js</code> library.
We recommend that you copy the files that you need into your project, so that you can adjust how they refer to the GoJS library
that you choose and so that you can include them into your own building and packaging procedures.
</p>
<p>
More information can be found in the <a href="../intro/extensions.html">GoJS Intro</a>.
</p>
<p>
<a href="../samples/index.html#extensions">Related samples</a>
</p>
<hr>
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</body>
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