问题
I am trying to update content of my page for printing. I want to have labels (spans) for each input element (textboxes, lists, etc.) to prevent text-cutoff when printing. I want to make sure before printing that all these labels reflect the most up-to-date user entered values from their respective input fields.
My first idea was to just put a label after each textbox, and bind it with the same value on page render, and then hide/show the input or the label based on CSS media attribute. But then I also need to have onchange handlers for every input element to update its respective label every time its value is changed.
My next thought was to use onbeforeprint and some jQuery to update the labels on the fly with the current values all in one spot. Cleaner, centralized, more concise code.
But as far as I can tell, onbeforeprint and onafterprint are only supported in IE and Firefox. ... BUT ... every article or post I can find that talks about browser support for these two functions is from a good 4 or 5 years, or even more ago!
So I'm wondering, have Chrome and Safari added support for these two functions at any point in the past 5 years?
回答1:
The MDN page on onbeforeprint is marked as updated last Nov 14, 2013, and it says “no” for Chrome, Opera, and Safari, “(Yes)” for IE, and “6.0” for Firefox. This is consistent with the results of checking with the current Chrome (version 34) and the last Windows version (5.1.7) of Safari. No event is triggered on them, and in developer tools, no onbeforeprint listener is shown under “Event Listeners” in developer tools when onbeforeprint attribute is used.
There is a WebKit bug report from 2008 about lack of support to beforeprint and afterprint events, and there’s a suggested patch but also issues with it, and it does not seem to be making progress.
So the answer is “No.”
Cf. onbeforeprint and onafterprint is not working in Chrome and IE?
As regards to the possible followup question “What should I use instead, then?”, it should be posted as a new question, with sufficient details (including code) to describe the original problem – in particular, what would be the part that you cannot do by using a print stylesheet.
回答2:
Whilst the above answers are excellent in answering the direct question the omit the following essential information:
Whilst the specific onbeforeprint and onafterprint events are not universally supported, there is functional support for the conceptual events - it IS possible to execute code before and after printing in most modern browsers.
See here for full details: http://tjvantoll.com/2012/06/15/detecting-print-requests-with-javascript/
Summary:
There exists a window.watchMedia API which allows you to hook into the transition events of CSS media queries, including the 'print' media query. This allows you to hook into events occurring immediately before and immediately after you print a page.
This API is well supported by Chrome and Webkit, and the onbeforeprint and onafterprint events are supported in IE and Firefox giving you pretty good coverage.
回答3:
From MDN onbeforeprint:
Well you can always add one event handler to listen for changes and handle updating the content. This is the basic idea [not cross browser friendly]
document.body.addEventListener("change", function(e){
var elem = e.target || e.srcElement;
elem.nextSibling.innerHTML = elem.value;
});
JSFiddle: http://jsfiddle.net/y4MGE/
You can use the print style sheet to hide the textboxes when printed and show whatever you want in its place.
来源：https://stackoverflow.com/questions/22969552/do-modern-browsers-support-onbeforeprint-onafterprint-html-events