How to add dashed stroke to a Triangle using FabricJS?

In this tutorial, we are going to learn how to add a dashed stroke to a Triangle using FabricJS. Triangle is one of the various shapes provided by FabricJS. In order to create a Triangle, we will have to create an instance of fabric.Triangle class and add it to the canvas. The strokeDashArray property allows us to specify a dash pattern for the object's stroke.

Syntax

new fabric.Triangle( { strokeDashArray: Array }: Object)

Parameters

options (optional) − This parameter is an Object which provides additional customizations to our triangle. Using this parameter, properties such as colour, cursor, stroke width, and a lot of other properties can be changed related to the object of which strokeDashArray is a property.

Options Keys

strokeDashArray − This property accepts an Array which allows us to specify a dash pattern for the object's stroke. For example, if we pass an array with values [2,3], it means a dash pattern of 2px dash and 3px gap and repeating this pattern infinitely.

Example 1

Default appearance of an object's stroke

Let's see a code example that depicts the default appearance of the stroke of a triangle object. Since we have not used the strokeDashArray property, there is no dash pattern being displayed.

<!DOCTYPE html>
<html>
<head>
   <!-- Adding the Fabric JS Library-->
   <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head>
<body>
   <h2>Default appearance of an object's stroke</h2>
   <p>You can see there is no dash pattern in the stroke</p>
   <canvas id="canvas"></canvas>
   <script>

      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);
   
      // Initiate a triangle object
      var triangle = new fabric.Triangle({
         left: 150,
         top: 30,
         width: 90,
         height: 80,
         fill: "#b0e0e6",
         stroke: "#5f9ea0",
         strokeWidth: 7,
      });

      // Add it to the canvas
      canvas.add(triangle);
   </script>
</body>
</html>

Example 2

Passing strokeDashArray property as key

In this example, we are passing the strokeDashArray property a value of [9,2]. This means that a dash pattern will be created such that there is a 9px long line, followed by a 2px gap, then again a 9px long line will be drawn and so on.

<!DOCTYPE html>
<html>
<head>
   <!-- Adding the Fabric JS Library-->
   <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head>
<body>
   <h2>Passing strokeDashArray property as key</h2>
   <p>You can see there is a dash pattern in the stroke now</p>
   <canvas id="canvas"></canvas>
   <script>
      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);

      // Initiate a triangle object
      var triangle = new fabric.Triangle({
         left: 150,
         top: 30,
         width: 90,
         height: 80,
         fill: "#b0e0e6",
         stroke: "#5f9ea0",
         strokeWidth: 7,
         strokeDashArray: [9, 2],
      });

      // Add it to the canvas
      canvas.add(triangle);
   </script>
</body>
</html>