如何查询与window.print()相关的所有JavaScript内置函数？

Great question! When you call window.print() to trigger the browser's print functionality, it kicks off a sequence of events you can hook into using these built-in event handlers:

• window.onbeforeprint: This function runs right before the print dialog pops up. It’s perfect for making print-specific tweaks—like hiding non-essential UI elements, applying print-only CSS, or resizing content to fit paper layouts—so your page looks polished in the print preview.
• window.onprint: Support for this one is inconsistent across browsers. In some implementations, it fires when the print dialog appears, but it’s not as reliably supported as the before/after handlers. For most use cases, stick with onbeforeprint and onafterprint instead.
• window.onafterprint: This handler executes after the print dialog closes, whether the user printed the page or canceled the action. Use it to revert any changes you made in onbeforeprint (like restoring hidden elements or switching back to your original page styles).

If you want to uncover every print-related built-in available in your browser, here are a few straightforward methods:

1. Filter the window object in DevTools

   • Open your browser’s DevTools (press F12 or Ctrl+Shift+I on Windows/Linux, Cmd+Opt+I on Mac)
   • Switch to the Console tab
   • Run this command: Object.keys(window).filter(key => key.toLowerCase().includes('print'))
     This will return all properties and methods on the window object that include "print" in their name—including the handlers you mentioned, plus any browser-specific additions (like experimental features).
   • For a more visual deep dive, type dir(window) in the console to see the full hierarchy of the window object, then use DevTools’ search bar to look for "print" entries.

2. Use DevTools’ built-in documentation

   • In the Console tab, type window.onbeforeprint and hover over the result. Most modern browsers will show a tooltip with a summary of the handler, and you can right-click it to select "Go to definition" for deeper details about the API and related functions.

3. Check the official Web API specification

   • The core print-related APIs are defined in the Web API spec. You can search within the spec (directly in your browser or offline copies) for terms like "print event handlers" to find the standardized set of functions, along with any experimental features supported in specific browsers.

内容的提问来源于stack exchange，提问作者Pax