Provide custom onLoadingStart and onLoadingEnd hooks

[steveklebanoff]

See #98

[steveklebanoff]

@crabbly can you let me know when this is published to npm? 😄

[crabbly]

@steveklebanoff Done! :)

[steveklebanoff]

@crabbly Awesome. Is http://printjs.crabbly.com/ open source? Would be good to update the Configuration

[crabbly]

Yes it is. The same repository, under the gh-pages branch.

[9585999]

these hooks work fine when the file type is pdf, if I want to show a preloader when I get data type html, then the modal window does not work properly, although it was not superfluous, because when using targetStyles: ["*"] is present a significant delay of 1-2 seconds before the appearance of the print window ...

[crabbly]

Hey @9585999 , the loading modal was initially intended to be used with PDF loading, but it does apply for any printing type. However, we may have to apply a promise in html.js to proceed only after all html elements styles were processed.

The problem with targetStyles: ["*"] may be related to either with large / complex html or slow machines. This feature was intended to print small parts / sections of html. Processing every style applied to each element is not the best solution. I'm working on another solution for html printing, which will not require all this style processing with javascript. This will also support CSS media queries, which is a great plus.

In the meantime, adding a promise to html.js would be nice. I will try to get to it if I can. A PR would be very welcome.