CanvasRenderingContext2D: lineDashOffset property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The CanvasRenderingContext2D.lineDashOffset property of the Canvas 2D API sets the line dash offset, or "phase."

Note: Lines are drawn by calling the stroke() method.

Value

A float specifying the amount of the line dash offset. The default value is 0.0.

Examples

Offsetting a line dash

This example draws two dashed lines. The first has no dash offset. The second has a dash offset of 4.

HTML

html
<canvas id="canvas"></canvas>

JavaScript

js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");

ctx.setLineDash([4, 16]);

// Dashed line with no offset
ctx.beginPath();
ctx.moveTo(0, 50);
ctx.lineTo(300, 50);
ctx.stroke();

// Dashed line with offset of 4
ctx.beginPath();
ctx.strokeStyle = "red";
ctx.lineDashOffset = 4;
ctx.moveTo(0, 100);
ctx.lineTo(300, 100);
ctx.stroke();

Result

The line with a dash offset is drawn in red.

Marching ants

The marching ants effect is an animation technique often found in selection tools of computer graphics programs. It helps the user to distinguish the selection border from the image background by animating the border.

js
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
let offset = 0;

function draw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.setLineDash([4, 2]);
  ctx.lineDashOffset = offset;
  ctx.strokeRect(10, 10, 100, 100);
}

function march() {
  offset++;
  if (offset > 5) {
    offset = 0;
  }
  draw();
  setTimeout(march, 20);
}

march();

Specifications

Specification
HTML
# dom-context-2d-linedashoffset-dev

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
lineDashOffset

Legend

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Full support
Full support
Uses a non-standard name.
Has more compatibility info.

See also