Understanding Node zIndex

What is zIndex of a node?

You can get/set zIndex of a node in this way:

// get
const zIndex = shape.zIndex();

// set
shape.zIndex(1);

zIndex is just the index of a node in its parent's children array. Please don't confuse zIndex in Konva with z-index in CSS.

const group = new Konva.Group();
const circle = new Konva.Circle({});
group.add(circle);

// it will log 0
console.log(circle.zIndex());

// the next line will not work because the group has only one child
circle.zIndex(1);

// still logs 0
console.log(circle.zIndex());

// for any node this equation will be true:
console.log(circle.zIndex() === circle.getParent().children.indexOf(circle));

You can't use zIndex to set absolute position of the node, like we do in CSS. Konva draws nodes in the strict order as they are defined in the nodes tree.

Instructions: Try to change zIndex of shapes using the buttons. Notice how the order of shapes changes.

Vanilla

import Konva from 'konva';

const width = window.innerWidth;
const height = window.innerHeight;

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

const layer = new Konva.Layer();

// first group
const group1 = new Konva.Group();
layer.add(group1);

const blackRect = new Konva.Rect({
x: 10,
y: 10,
width: 100,
height: 100,
fill: 'black',
});
group1.add(blackRect);

const redCircle = new Konva.Circle({
x: 80,
y: 80,
radius: 40,
fill: 'red',
});
group1.add(redCircle);

// second group
const group2 = new Konva.Group();
layer.add(group2);

const greenRect = new Konva.Rect({
x: 50,
y: 50,
width: 100,
height: 100,
fill: 'green',
});
group2.add(greenRect);

stage.add(layer);

// create buttons
const btn1 = document.createElement('button');
btn1.textContent = 'Move red circle to group2';
btn1.addEventListener('click', () => {
redCircle.moveTo(group2);
});

const btn2 = document.createElement('button');
btn2.textContent = 'Move red circle to group1';
btn2.addEventListener('click', () => {
redCircle.moveTo(group1);
});

document.body.appendChild(btn1);
document.body.appendChild(btn2);

React

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

const App = () => {
  const [redCircleGroup, setRedCircleGroup] = useState('group1');

  return (
    <>
      <button onClick={() => setRedCircleGroup('group2')}>
        Move red circle to group2
      </button>
      <button onClick={() => setRedCircleGroup('group1')}>
        Move red circle to group1
      </button>
      <Stage width={window.innerWidth} height={window.innerHeight}>
        <Layer>
          <Group>
            <Rect
              x={10}
              y={10}
              width={100}
              height={100}
              fill="black"
            />
            {redCircleGroup === 'group1' && (
              <Circle
                x={80}
                y={80}
                radius={40}
                fill="red"
              />
            )}
          </Group>
          <Group>
            <Rect
              x={50}
              y={50}
              width={100}
              height={100}
              fill="green"
            />
            {redCircleGroup === 'group2' && (
              <Circle
                x={80}
                y={80}
                radius={40}
                fill="red"
              />
            )}
          </Group>
        </Layer>
      </Stage>
    </>
  );
};

export default App;

Vue

<template>
  <div>
    <button @click="moveToGroup2">Move red circle to group2</button>
    <button @click="moveToGroup1">Move red circle to group1</button>
    <v-stage :config="stageSize">
      <v-layer>
        <v-group>
          <v-rect :config="blackRectConfig" />
          <v-circle v-if="redCircleGroup === 'group1'" :config="redCircleConfig" />
        </v-group>
        <v-group>
          <v-rect :config="greenRectConfig" />
          <v-circle v-if="redCircleGroup === 'group2'" :config="redCircleConfig" />
        </v-group>
      </v-layer>
    </v-stage>
  </div>
</template>

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

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

const redCircleGroup = ref('group1');

const blackRectConfig = {
  x: 10,
  y: 10,
  width: 100,
  height: 100,
  fill: 'black'
};

const greenRectConfig = {
  x: 50,
  y: 50,
  width: 100,
  height: 100,
  fill: 'green'
};

const redCircleConfig = {
  x: 80,
  y: 80,
  radius: 40,
  fill: 'red'
};

const moveToGroup2 = () => {
  redCircleGroup.value = 'group2';
};

const moveToGroup1 = () => {
  redCircleGroup.value = 'group1';
};
</script>