svelte-konva

svelte-konva

svelte-konva is a component-based svelte wrapper for the Konva HTML5 2D canvas library. For further information and examples please visit the docs.

Compatibility

Currently compatible with Svelte v3 & 4, SvelteKit v1 and Konva v8 & 9.

Install

npm i svelte-konva konva

Quick start

<script>
  import { Stage, Layer, Rect } from 'svelte-konva';
</script>

<Stage config={{ width: 1000, height: 1000 }}>
  <Layer>
    <Rect config={{ x: 100, y: 100, width: 400, height: 200, fill: 'blue' }} />
  </Layer>
</Stage>

Events

You can listen to Konva events by using the Svelte on:event Syntax. All Konva events are supported.

<script>
  import { Stage, Layer, Rect } from 'svelte-konva';

  function handleClick(e) {
    const konvaEvent = e.detail;
    window.alert(`Clicked on rectangle: ${konvaEvent.type}`);
  }
</script>

<Stage config={{ width: 1000, height: 1000 }}>
  <Layer>
    <Rect
      config={{ x: 100, y: 100, width: 400, height: 200, fill: 'blue' }}
      on:pointerclick={handleClick}
    />
  </Layer>
</Stage>

Accessing the underlying Konva node

In various cases it is useful and required to be able to access the underlying Konva node object. In svelte-konva you can do this by binding the handle prop.

<script>
  import { onMount, tick } from 'svelte';
  import { Stage, Layer, Rect } from 'svelte-konva';

  let rectangle;

  onMount(async () => {
    // Wait for dom update so the rectangle handle becomes defined
    await tick();

    const json = rectangle.toJSON();
    window.alert(`Rectangle as JSON: ${json}`);
  });
</script>

<Stage config={{ width: 1000, height: 1000 }}>
  <Layer>
    <Rect
      config={{ x: 100, y: 100, width: 400, height: 200, fill: 'blue' }}
      bind:handle={rectangle}
    />
  </Layer>
</Stage>

Binding the config prop

By default svelte-konva keeps your config in sync (position, rotation, scale, etc.) with the Konva node after dragend and transformend events. If you bind the config prop any reactive blocks depending on the config will also be triggered once such changes happen. In case you don't want svelte-konva to sync those changes you can pass the staticConfig prop to the component.

<script>
  import { Stage, Layer, Rect } from 'svelte-konva';

  let rectangleConfig = {
    x: 100,
    y: 100,
    width: 400,
    height: 200,
    fill: 'blue',
    draggable: true
  };

  $: console.log(
    `Rectangle was dragged. New x: ${rectangleConfig.x}. New y: ${rectangleConfig.y}.`
  );
</script>

<Stage config={{ width: 1000, height: 1000 }}>
  <Layer>
    <Rect bind:config={rectangleConfig} />
  </Layer>
</Stage>

Usage with SvelteKit

Generally svelte-konva is a client-side only library. When using SvelteKit, special care needs to be taken if svelte-konva/Konva functionality is used on prerendered and server side rendered (SSR) components. Prerendering and SSR happens in a Node.js environment which causes Konva to require the canvas library as Konva can also be used in Node.js environments. When you use svelte-konva in such conditions you'll likely run into the following error:

Error: Cannot find module 'canvas'

There are multiple solutions to this problem:

Installing canvas:

Simplest solution is to install canvas:

npm i canvas

This will satisfy the canvas dependency of Konva and you can use svelte-konva components in prerendered and SSR SvelteKit pages. The solution is a bit messy though, as you now have installed a package you don't really need which adds unnecessary overhead. Alternatively use one of the following solutions:

Dynamically import your svelte-konva stage:

A better approach is to dynamically import your svelte-konva canvas on the client-side only. Suppose you have a Svelte component containing your stage with various svelte-konva components:

MyCanvas.svelte

<script>
  import { Stage, Layer, Rect } from 'svelte-konva';
  import OtherComponentUsingSvelteKonva from './OtherComponentUsingSvelteKonva.svelte';

  const rectangleConfig = {
    /*...*/
  };
</script>

<Stage config={{ width: 1000, height: 1000 }}>
  <Layer>
    <Rect bind:config={rectangleConfig} />

    <OtherComponentUsingSvelteKonva />
  </Layer>
</Stage>

To use this component inside a SvelteKit prerendered/SSR page you can dynamically import it inside onMount() and render it using <svelte:component>:

+page.svelte

<script>
  import { onMount } from 'svelte';
  // typescript:
  // import type MyCanvasComponent from '$lib/MyCanvas.svelte';

  let MyCanvas;
  // typescript:
  // let MyCanvas: typeof MyCanvasComponent;

  onMount(async () => {
    // Dynamically import your canvas component encapsulating all svelte-konva functionality inside onMount()
    MyCanvas = (await import('$lib/MyCanvas.svelte')).default;
  });
</script>

<div>
  <p>This is my fancy server side rendered (or prerendered) page.</p>

  <!-- Use your dynamically imported svelte-konva canvas component with a svelte:component block, you can pass any component props as usual -->
  <svelte:component this={MyCanvas} someProp="SomeString" />
</div>

Dynamically import svelte-konva using vite:

The vite-plugin-iso-import allows you to make client-side only imports without needing the manual approach in onMount() described above. Please follow the installation instructions in the README then you can dynamically import your component like so:

+page.svelte

<script>
  import MyCanvasComponent from '$lib/MyCanvas.svelte?client'; // Client-side only import

  // Set component variable to null if page is rendered in SSR, otherwise use client-side only import
  let MyCanvas = import.meta.env.SSR ? null : MyCanvasComponent;
</script>

<div>
  <p>This is my fancy server side rendered (or prerendered) page.</p>

  <!-- Use your dynamically imported svelte-konva canvas component with a svelte:component block, you can pass any component props as usual -->
  <svelte:component this={MyCanvas} someProp="SomeString" />
</div>

Currently vite-plugin-iso-import cannot automatically fix intellisense inside .svelte files with TypeScript. Consult the README for a workaround to this problem.

For further examples please consult the docs or clone the repo and run npm i && npm run examples.

Changelog

Please refer to the CHANGELOG.md or releases page.

Changelog

v0.3.1

Version bump to update README, functionality remains unchanged

• Added SvelteKit instructions to README.md
• Various dependency updates