cancel()
方法在
ReadableStreamDefaultReader
interface cancels the stream, signaling a loss of interest in the stream by a consumer. The supplied reason argument will be given to the underlying source, which may or may not use it.
Cancel is used when you've completely finished with the stream and don't need any more data from it, even if there are chunks enqueued waiting to be read. That data is lost after cancel is called, and the stream is not readable any more. To read those chunks still and not completely get rid of the stream, you'd use
ReadableStreamDefaultController.close()
.
cancel()
method behaves the same as that for the associated stream (
ReadableStream.cancel()
).
var promise = readableStreamDefaultReader.cancel(reason);
DOMString
providing a human-readable reason for the cancellation.
A
Promise
, which fulfills with the value given in the
reason
参数。
ReadableStreamDefaultReader
, or the stream has no owner.
In the following simple example, a previously-created custom
ReadableStream
is read using a
ReadableStreamDefaultReader
created using
getReader()
. (this code is based on our
Simple random stream example
). Each chunk is read sequentially and output to the UI, until the stream has finished being read, at which point we return out of the recursive function and print the entire stream to another part of the UI.
When the stream is done (
if (done)
), we run
reader.cancel()
to cancel the stream, signalling that we don't need to use it any more.
function fetchStream() {
const reader = stream.getReader();
let charsReceived = 0;
// read() returns a promise that resolves
// when a value has been received
reader.read().then(function processText({ done, value }) {
// Result objects contain two properties:
// done - true if the stream has already given you all its data.
// value - some data. Always undefined when done is true.
if (done) {
console.log("Stream complete");
reader.cancel();
para.textContent = result;
return;
}
// value for fetch streams is a Uint8Array
charsReceived += value.length;
const chunk = value;
let listItem = document.createElement('li');
listItem.textContent = 'Received ' + charsReceived + ' characters so far. Current chunk = ' + chunk;
list2.appendChild(listItem);
result += chunk;
// Read some more, and call this function again
return reader.read().then(processText);
});
}
| 规范 | 状态 | 注释 |
|---|---|---|
|
流
The definition of 'cancel()' in that specification. |
实时标准 | 初始定义。 |
| 桌面 | 移动 | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
cancel
|
Chrome ? | Edge ? |
Firefox
65
|
IE ? | Opera ? | Safari ? | WebView Android ? | Chrome Android ? |
Firefox Android
65
|
Opera Android ? | Safari iOS ? | Samsung Internet Android ? |
完整支持
兼容性未知
实验。期望将来行为有所改变。
用户必须明确启用此特征。
ReadableStreamDefaultReader
cancel()
read()
releaseLock()