---
title: Chain theory
---

<p>
    When 2 or more paths connect end to end, we call this a <b>chain</b>. 
    Here are 3 lines that connect end to end, forming a chain with 3 links; 
    each line path is considered a link in the chain:
</p>

<script>
//render a model with paths that form a chain

var makerjs = require('makerjs');

var model = {
  paths: {
    "0": new makerjs.paths.Line([0, 0], [100, 0]),
    "1": new makerjs.paths.Line([100, 0], [100, 100]),
    "2": new makerjs.paths.Line([100, 100], [200, 100]),
  }
};

var svg = makerjs.exporter.toSVG(model);

document.write(svg);
</script>

<p>
    When the links do not have any loose ends and connect to each other, we call this an <b>endless</b> chain.
    Frequently, endless chains are used to represent a <i>closed geometry</i>.
    Here is an endless chain made up of 2 lines and an arc:
</p>

<script>
//render a model with paths that form an endless chain

var makerjs = require('makerjs');

var model = {
  paths: {
    "v": new makerjs.paths.Line([0, 0], [0, 100]),
    "h": new makerjs.paths.Line([0, 0], [100, 0]),
    "arc":new makerjs.paths.Arc([0, 0], 100, 0, 90)
  }
};

var svg = makerjs.exporter.toSVG(model);

document.write(svg);
</script>

<p>
    A circle is a closed geometry by nature. In Maker.js, a single circle comprises an endless chain with only one link. 
</p>

<script>
    //render a circle
    
    var makerjs = require('makerjs');
    
    var svg = makerjs.exporter.toSVG(new makerjs.paths.Circle(50));
    
    document.write(svg);
</script>
        
<p>
    A chain may contain other chains, recursively. A chain may only contain others if it is an endless chain itself.
    Here are some examples of one chain containing another:
</p>

<script>
//render a ring

var makerjs = require('makerjs');

var model = {
    models: {
        ring: new makerjs.models.Ring(15, 7),
        plate: makerjs.model.moveRelative(
            {
                models: {
                    outer: makerjs.model.center(new makerjs.models.Rectangle(60, 30)),
                    inner: makerjs.model.center(new makerjs.models.Oval(45, 15))
                }
            },
            [60, 0]
        )
    }
};

var svg = makerjs.exporter.toSVG(model);

document.write(svg);
</script>

<p>
    Here is a model which does <b>not</b> have any chains. Although the lines overlap, they do not connect end to end.
</p>

<script>
var makerjs = require('makerjs');

var model = {
  paths: {
    "h1": new makerjs.paths.Line([0, 10], [30, 10]),
    "h2": new makerjs.paths.Line([0, 20], [30, 20]),
    "v1": new makerjs.paths.Line([10, 0], [10, 30]),
    "v2": new makerjs.paths.Line([20, 0], [20, 30])
  }
};

var svg = makerjs.exporter.toSVG(model);

document.write(svg);
</script>

<h4>Chains are implicit</h4>

You do not explicitly define chains in your drawing, chains are something that Maker.js <i>finds</i> in your model(s).

<h4>Finding</h4>

Call one of these two functions to find chains, which will return one or more <b>Chain</b> objects:

<ul>
    <li><a href="/docs/api/modules/makerjs.model.html#findsinglechain">makerjs.model.findSingleChain(model)</a></li>
    <li><a href="/docs/api/modules/makerjs.model.html#findchains">makerjs.model.findChains(model)</a></li>
</ul>

<h4>Chain object type</h4>

{% include object-type.html type=site.data.project.Interface.IChain %}