DOMContentLoaded事件是當document被完整的讀取跟解析後就會被觸發,不會等待 stylesheets, 圖片和subframes完成讀取 (load事件可以用來作為判斷頁面已經完整讀取的方法).
Note: Stylesheet loads block script execution, 如果 <script> 被放在 <link rel="stylesheet" ...>後面的話, 須等到前面的stylesheet載入並完成解析，此時 DOMContentLoaded才會被觸發。
Speeding up
If you want DOM to get parsed as fast as possible after the user had requested the page, some things you could do is turn your JavaScript asynchronous and to optimize loading of stylesheets which if used as usual, slow down page load due to being loaded in parallel, "stealing" traffic from the main html document.
General info
- Specification
- HTML5
- Interface
- Event
- Bubbles
- Yes
- Cancelable
- Yes (although specified as a simple event that isn't cancelable)
- Target
- Document
- Default Action
- None.
屬性
| Property | Type | Description |
|---|---|---|
target Read only |
EventTarget |
The event target (the topmost target in the DOM tree). |
type Read only |
DOMString |
The type of event. |
bubbles Read only |
Boolean |
Whether the event normally bubbles or not |
cancelable Read only |
Boolean |
Whether the event is cancellable or not? |
瀏覽器相容性
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 0.2 | 1.0 (1.7 or earlier) | 9.0 | 9.0 | 3.1 |
| Feature | Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|
| Basic support | (Yes) | 1.0 (1) | ? | (Yes) | (Yes) |
Bubbling for this event is supported by at least Gecko 1.9.2, Chrome 6, and Safari 4.
Cross-browser fallback
Internet Explorer 8 supports the <code>readystatechange</code> event, which can be used to detect that the DOM is ready. In earlier version of Internet Explorer, this state can be detected by regularily trying to execute <code>document.documentElement.doScroll("left");</code>, as this snippet will throw an error until the DOM is ready.
General-purpose JS libraries such as jQuery offer cross-browser methods to detect that the DOM is ready. There are also standalone scripts that offer this feature : contentloaded.js (supports only one listener) and jquery.documentReady.js (doesn't depend on jQuery, despite its name).