Javascript – Capture HTML Canvas as gif/jpg/png/pdf

canvasexporthtmljavascriptpng

Is it possible to capture or print what's displayed in an html canvas as an image or pdf?

I'd like to generate an image via canvas, and be able to generate a png from that image.

Best Answer

Oops. Original answer was specific to a similar question. This has been revised:

var canvas = document.getElementById("mycanvas");
var img    = canvas.toDataURL("image/png");

with the value in IMG you can write it out as a new Image like so:

document.write('<img src="'+img+'"/>');

Dynamically create `<input>`s in a form and submit it

/**
 * sends a request to the specified url from a form. this will change the window location.
 * @param {string} path the path to send the post request to
 * @param {object} params the parameters to add to the url
 * @param {string} [method=post] the method to use on the form
 */

function post(path, params, method='post') {

  // The rest of this code assumes you are not using a library.
  // It can be made less verbose if you use one.
  const form = document.createElement('form');
  form.method = method;
  form.action = path;

  for (const key in params) {
    if (params.hasOwnProperty(key)) {
      const hiddenField = document.createElement('input');
      hiddenField.type = 'hidden';
      hiddenField.name = key;
      hiddenField.value = params[key];

      form.appendChild(hiddenField);
    }
  }

  document.body.appendChild(form);
  form.submit();
}

Example:

post('/contact/', {name: 'Johnny Bravo'});

EDIT: Since this has gotten upvoted so much, I'm guessing people will be copy-pasting this a lot. So I added the hasOwnProperty check to fix any inadvertent bugs.

Javascript – How to you encode a string to Base64 in JavaScript

You can use btoa() and atob() to convert to and from base64 encoding.

There appears to be some confusion in the comments regarding what these functions accept/return, so…

btoa() accepts a “string” where each character represents an 8-bit byte – if you pass a string containing characters that can’t be represented in 8 bits, it will probably break. This isn’t a problem if you’re actually treating the string as a byte array, but if you’re trying to do something else then you’ll have to encode it first.
atob() returns a “string” where each character represents an 8-bit byte – that is, its value will be between 0 and 0xff. This does not mean it’s ASCII – presumably if you’re using this function at all, you expect to be working with binary data and not text.

Best Answer

Related Solutions

JavaScript post request like a form submit

Dynamically create <input>s in a form and submit it

Javascript – How to you encode a string to Base64 in JavaScript

See also:

Related Topic

Dynamically create `<input>`s in a form and submit it