HTML5 Canvas Listening False Performance Tip

If you have a lot of shapes on the canvas and you don't need to detect events for some of them, you can set listening to false to improve performance.

When listening = false, the shape will be ignored from event detection (like mouseover, drag and drop, click, etc). This can significantly improve performance for complex applications.

Below is a demo showing the performance difference between listening and non-listening shapes:

Vanilla

import Konva from 'konva';

const stage = new Konva.Stage({
  container: 'container',
  width: window.innerWidth,
  height: window.innerHeight,
});

const layer = new Konva.Layer();
stage.add(layer);

// Create many circles with listening enabled
for (let i = 0; i < 100; i++) {
  const circle = new Konva.Circle({
    x: Math.random() * stage.width(),
    y: Math.random() * stage.height(),
    radius: 20,
    fill: 'blue',
    opacity: 0.5,
    // Enable event detection (default)
    listening: true,
  });
  
  // Add hover effect
  circle.on('mouseover', function() {
    this.fill('red');
    layer.draw();
  });
  
  circle.on('mouseout', function() {
    this.fill('blue');
    layer.draw();
  });
  
  layer.add(circle);
}

// Create many circles with listening disabled
for (let i = 0; i < 1000; i++) {
  const circle = new Konva.Circle({
    x: Math.random() * stage.width(),
    y: Math.random() * stage.height(),
    radius: 20,
    fill: 'green',
    opacity: 0.5,
    // Disable event detection for better performance
    listening: false,
  });
  layer.add(circle);
}

// Add text explanation
const text = new Konva.Text({
  x: 10,
  y: 10,
  text: 'Blue circles (100) have event listeners (hover them)\nGreen circles (1000) have no listeners (better performance)',
  fontSize: 16,
  fill: 'black',
});
layer.add(text);

layer.draw();

Open Sandbox

React

import { Stage, Layer, Circle, Text } from 'react-konva';
import { useState } from 'react';

const App = () => {
  const [hoveredId, setHoveredId] = useState(null);
  
  // Generate circles data
  const listeningCircles = Array.from({ length: 100 }, (_, i) => ({
    id: i,
    x: Math.random() * window.innerWidth,
    y: Math.random() * window.innerHeight,
  }));
  
  const nonListeningCircles = Array.from({ length: 1000 }, (_, i) => ({
    id: i + 100,
    x: Math.random() * window.innerWidth,
    y: Math.random() * window.innerHeight,
  }));

  return (
    <Stage width={window.innerWidth} height={window.innerHeight}>
      <Layer>
        {/* Circles with event listeners */}
        {listeningCircles.map((circle) => (
          <Circle
            key={circle.id}
            x={circle.x}
            y={circle.y}
            radius={20}
            fill={hoveredId === circle.id ? 'red' : 'blue'}
            opacity={0.5}
            onMouseEnter={() => setHoveredId(circle.id)}
            onMouseLeave={() => setHoveredId(null)}
          />
        ))}
        
        {/* Circles without event listeners */}
        {nonListeningCircles.map((circle) => (
          <Circle
            key={circle.id}
            x={circle.x}
            y={circle.y}
            radius={20}
            fill="green"
            opacity={0.5}
            listening={false}
          />
        ))}
        
        <Text
          x={10}
          y={10}
          text="Blue circles (100) have event listeners (hover them)\nGreen circles (1000) have no listeners (better performance)"
          fontSize={16}
          fill="black"
        />
      </Layer>
    </Stage>
  );
};

export default App;

Open Sandbox

Vue

<template>
  <v-stage :config="stageSize">
    <v-layer>
      <!-- Circles with event listeners -->
      <v-circle
        v-for="circle in listeningCircles"
        :key="circle.id"
        :config="getListeningCircleConfig(circle)"
        @mouseenter="handleMouseEnter(circle.id)"
        @mouseleave="handleMouseLeave"
      />
      
      <!-- Circles without event listeners -->
      <v-circle
        v-for="circle in nonListeningCircles"
        :key="circle.id"
        :config="getNonListeningCircleConfig(circle)"
      />
      
      <v-text :config="textConfig" />
    </v-layer>
  </v-stage>
</template>

<script setup>
import { ref } from 'vue';

const stageSize = {
  width: window.innerWidth,
  height: window.innerHeight
};

const hoveredId = ref(null);

// Generate circles data
const listeningCircles = Array.from({ length: 100 }, (_, i) => ({
  id: i,
  x: Math.random() * window.innerWidth,
  y: Math.random() * window.innerHeight,
}));

const nonListeningCircles = Array.from({ length: 1000 }, (_, i) => ({
  id: i + 100,
  x: Math.random() * window.innerWidth,
  y: Math.random() * window.innerHeight,
}));

const getListeningCircleConfig = (circle) => ({
  x: circle.x,
  y: circle.y,
  radius: 20,
  fill: hoveredId.value === circle.id ? 'red' : 'blue',
  opacity: 0.5,
});

const getNonListeningCircleConfig = (circle) => ({
  x: circle.x,
  y: circle.y,
  radius: 20,
  fill: 'green',
  opacity: 0.5,
  listening: false,
});

const textConfig = {
  x: 10,
  y: 10,
  text: 'Blue circles (100) have event listeners (hover them)\nGreen circles (1000) have no listeners (better performance)',
  fontSize: 16,
  fill: 'black',
};

const handleMouseEnter = (id) => {
  hoveredId.value = id;
};

const handleMouseLeave = () => {
  hoveredId.value = null;
};
</script>

Open Sandbox