WindowEventHandlers.onbeforeprint

WindowEventHandlers mixin 的 onbeforeprint 属性是用于处理当前 window 的 beforeprint 事件的事件处理器（EventHandler）。These events are raised before the print dialog window is opened.

The beforeprint and afterprint events allow pages to change their content before printing starts (perhaps to remove a banner, for example) and then revert those changes after printing has completed. In general, you should prefer the use of an @media print CSS at-rule, but it may be necessary to use these events in some cases.

语法

window.addEventListener("beforeprint", function(event) { ... });
window.onbeforeprint = function(event) { ... };

Polyfill

一些基于 Webkit 内核的浏览器，比如 Safari，没有实现这些事件，但是你可以通过 window.matchMedia('print').得到与 beforeprint 事件等价的效果。

var mediaQueryList = window.matchMedia('print');
mediaQueryList.addListener(function(mql) {
  if(mql.matches) {
    console.log('webkit equivalent of onbeforeprint');
  }
});

规范

浏览器兼容性

相关链接

• Window.print()
• WindowEventHandlers.onafterprint
• 打印