CanvasRenderingContext2D.lineWidth

The CanvasRenderingContext2D.lineWidth property of the Canvas 2D API sets the thickness of lines in space units. When getting, it returns the current value (1.0 by default). When setting, zero, negative, Infinity and NaN values are ignored; otherwise the current value is set to the new value.

See also the chapter Applying styles and color in the Canvas Tutorial.

Syntax

ctx.lineWidth = value;

Options

value

A number specifying the line width in space units. Zero, negative, Infinity and NaN values are ignored.

Examples

Using the lineWidth property

This is just a simple code snippet using the lineWidth property to draw lines with a rounded end.

HTML

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

JavaScript

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineWidth = 15;
ctx.lineTo(100, 100);
ctx.stroke();

Edit the code below and see your changes update live in the canvas:

<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.beginPath();
ctx.moveTo(0,0);
ctx.lineWidth = 15;
ctx.lineTo(100, 100);
ctx.stroke();</textarea>

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var textarea = document.getElementById('code');
var reset = document.getElementById('reset');
var edit = document.getElementById('edit');
var code = textarea.value;
function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}
reset.addEventListener('click', function() {
  textarea.value = code;
  drawCanvas();
});
edit.addEventListener('click', function() {
  textarea.focus();
})
textarea.addEventListener('input', drawCanvas);
window.addEventListener('load', drawCanvas);

Specifications

Browser compatibility

WebKit/Blink-specific notes

• In WebKit- and Blink-based Browsers, a non-standard and deprecated method ctx.setLineWidth() is implemented besides this property.

Gecko-specific notes

• Starting Gecko 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1), setting lineWidth to a negative value no longer throws an exception; instead, it properly ignores non-positive values.

See also

• The interface defining it, CanvasRenderingContext2D
• CanvasRenderingContext2D.lineCap
• CanvasRenderingContext2D.lineJoin