Javascript Draw Line From Point To Point

Summary: in this tutorial, you'll learn how to draw a line using the Canvas API.

Steps for drawing a line in JavaScript

To draw a line on a canvas, you use the following steps:

First, create a new line by calling the beginPath() method.
Second, move the drawing cursor to the point (x,y) without drawing a line by calling the moveTo(x, y).
Finally, draw a line from the previous point to the point (x,y) by calling the lineTo(x,y) method.

Set the line stroke

If you want to stroke the line with the strokeStyle, you can call the stroke() method after calling the lineTo(x,y) method.

Set the line width

To set the width for a line, you use the lineWidth property of the 2D drawing context before calling stroke() method:

                          ctx.lineWidth = 10;

The lineTo(x,y) method

The lineTo(x,y ) method accepts both positive and negative arguments.

If thex is positive, the lineTo(x,y) method draws the line from the starting point to the right. Otherwise, it draws the line from the starting point to the left.

If they is positive, the lineTo(x,y) method draws the line from the starting point down the y-axis. Otherwise, it draws the line from the starting point up to the y-axis.

Drawing a line example

The following shows the index.html file that contains a canvas element:

                                          <!DOCTYPE                  html>                <html                  lang="en">                <head>                <meta                  charset="UTF-8">                <meta                  name="viewport"                  content="width=device-width, initial-scale=1.0">                <title>JavaScript - Drawing a Line</title>                <link                  rel="stylesheet"                  href="css/style.css">                </head>                <body>                <h1>JavaScript - Drawing a Line</h1>                <canvas                  id="canvas"                  height="400"                  width="500">                </canvas>                <script                  src="js/app.js">                </script>                </body>                </html>                          
                          Code language:              HTML, XML              (              xml              )

And this app.js contains that draws a line with the color red, 5-pixel width from the point (100, 100) to (300, 100):

                                                            function                  draw()                {                const                canvas =                document.querySelector('#canvas');                if                (!canvas.getContext) {                return;     }                const                ctx = canvas.getContext('2d');                // set line stroke and line width                ctx.strokeStyle =                'red';     ctx.lineWidth =                5;                // draw a red line                ctx.beginPath();     ctx.moveTo(100,                100);     ctx.lineTo(300,                100);     ctx.stroke();  } draw();            
                          Code language:              JavaScript              (              javascript              )

The following shows the output:

Here is the link that shows the canvas with the line.

Develop a resuable drawLine() function

The following drawLine() function draws a line from one point to another with a specified stroke and width:

                                                            function                  drawLine(ctx, begin, end, stroke =                    'black', width =                    1                  )                {                if                (stroke) {         ctx.strokeStyle = stroke;     }                if                (width) {         ctx.lineWidth = width;     }      ctx.beginPath();     ctx.moveTo(...begin);     ctx.lineTo(...end);     ctx.stroke(); }                          
                          Code language:              JavaScript              (              javascript              )

To draw a line from (100,100) to (100,300) with the line color green and line width 5 pixels, you can call the drawLine() function as follows:

                                          const                canvas =                document.querySelector('#canvas');                if                (canvas.getContext) {                const                ctx = canvas.getContext('2d');     drawLine(ctx, [100,                100], [100,                300],                'green',                5); }                          
                          Code language:              JavaScript              (              javascript              )

Summary

Use beginPath(), moveTo(x, y) and lineTo(x,y) to draw a line.
Use the strokeStyle and lineWidth to set the line stroke and line width.

Was this tutorial helpful ?