4.7 KiB
html2canvas
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JavaScript HTML renderer
The script allows you to take "screenshots" of webpages or parts of it, directly on the users browser. The screenshot is based on the DOM and as such may not be 100% accurate to the real representation as it does not make an actual screenshot, but builds the screenshot based on the information available on the page.
How does it work?
The script renders the current page as a canvas image, by reading the DOM and the different styles applied to the elements.
It does not require any rendering from the server, as the whole image is created on the client's browser. However, as it is heavily dependent on the browser, this library is not suitable to be used in nodejs. It doesn't magically circumvent any browser content policy restrictions either, so rendering cross-origin content will require a proxy to get the content to the same origin.
The script is still in a very experimental state, so I don't recommend using it in a production environment nor start building applications with it yet, as there will be still major changes made.
Browser compatibility
The library should work fine on the following browsers (with Promise polyfill):
- Firefox 3.5+
- Google Chrome
- Opera 12+
- IE9+
- Safari 6+
As each CSS property needs to be manually built to be supported, there are a number of properties that are not yet supported.
Usage
The html2canvas library utilizes Promises and expects them to be available in the global context. If you wish to
support older browsers that do not natively support Promises, please include a polyfill such as
es6-promise before including html2canvas.
Note! These instructions are for using the current dev version of 0.5, for the latest release version (0.4.1), checkout the old readme.
To render an element with html2canvas, simply call:
html2canvas(element[, options]);
The function returns a Promise containing the <canvas> element. Simply add a promise fullfillment handler to the promise using then:
html2canvas(document.body).then(function(canvas) {
document.body.appendChild(canvas);
});
Building
You can download ready builds here.
Clone git repository:
$ git clone git://github.com/niklasvh/html2canvas.git
Install dependencies:
$ npm install
Build browser bundle
$ npm run build
Running tests
The library has two sets of tests. The first set is a number of qunit tests that check that different values parsed by browsers are correctly converted in html2canvas. To run these tests with grunt you'll need phantomjs.
The other set of tests run Firefox, Chrome and Internet Explorer with webdriver. The selenium standalone server (runs on Java) is required for these tests and can be downloaded from here. They capture an actual screenshot from the test pages and compare the image to the screenshot created by html2canvas and calculate the percentage differences. These tests generally aren't expected to provide 100% matches, but while committing changes, these should generally not go decrease from the baseline values.
Start by downloading the dependencies:
$ npm install
Run tests:
$ npm test
Examples
For more information and examples, please visit the homepage or try the test console.
Contributing
If you wish to contribute to the project, please send the pull requests to the develop branch. Before submitting any changes, try and test that the changes work with all the support browsers. If some CSS property isn't supported or is incomplete, please create appropriate tests for it as well before submitting any code changes.