loadstart
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
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当程序开始加载时，loadstart 事件将被触发。这个事件可以被 XMLHttpRequest 调用，也适用于 <img> 和 <video> 元素。
基本信息
属性
| Property | Type | Description |
|---|---|---|
target 只读 |
EventTarget |
The event target (the topmost target in the DOM tree). |
type 只读 |
DOMString |
The type of event. |
bubbles 只读 |
Boolean |
Whether the event normally bubbles or not. |
cancelable 只读 |
Boolean |
Whether the event is cancellable or not. |
lengthComputable 只读 |
Boolean |
Specifies whether or not the total size of the transfer is known. Read only. |
loaded 只读 |
unsigned long (long) | The number of bytes transferred since the beginning of the operation. This doesn't include headers and other overhead, but only the content itself. Read only. |
total 只读 |
unsigned long (long) | The total number of bytes of content that will be transferred during the operation. If the total size is unknown, this value is zero. Read only. |
规范
| Specification |
|---|
| XMLHttpRequest Standard # event-xhr-loadstart |
| XMLHttpRequest Standard # handler-xhr-onloadstart |