ReadableStream.ReadableStream()

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ReadableStream() constructor creates and returns a readable stream object from the given handlers.

句法

var readableStream = new ReadableStream(underlyingSource[, queuingStrategy]);

参数

underlyingSource

An object containing methods and properties that define how the constructed stream instance will behave.


								underlyingSource

can contain the following:

start(controller): This is a method, called immediately when the object is constructed. The contents of this method are defined by the developer, and should aim to get access to the stream source, and do anything else required to set up the stream fuctionality. If this process is to be done asynchronously, it can return a promise to signal success or failure. The controller parameter passed to this method is a ReadableStreamDefaultController 或 ReadableByteStreamController , depending on the value of the type property. This can be used by the developer to control the stream during set up.
pull(controller) 可选: This method, also defined by the developer, will be called repeatedly when the stream's internal queue of chunks is not full, up until it reaches its high water mark. If pull() returns a promise, then it won't be called again until that promise fulfills; if the promise rejects, the stream will become errored. The controller parameter passed to this method is a ReadableStreamDefaultController 或 ReadableByteStreamController , depending on the value of the type property. This can be used by the developer to control the stream as more chunks are fetched.
cancel(reason) 可选: This method, also defined by the developer, will be called if the app signals that the stream is to be cancelled (e.g. if ReadableStream.cancel() is called). The contents should do whatever is necessary to release access to the stream source. If this process is asynchronous, it can return a promise to signal success or failure. The reason parameter contains a DOMString describing why the stream was cancelled.
type 可选: This property controls what type of readable stream is being dealt with. If it is included with a value set to "bytes" , the passed controller object will be a ReadableByteStreamController capable of handling a BYOB (bring your own buffer)/byte stream. If it is not included, the passed controller will be a ReadableStreamDefaultController .
autoAllocateChunkSize 可选: For byte streams, the developer can set the autoAllocateChunkSize with a positive integer value to turn on the stream's auto-allocation feature. With this turned on, the stream implementation will automatically allocate an ArrayBuffer with a size of the given integer, and the consumer can also use a default reader.

queuingStrategy 可选

An object that optionally defines a queuing strategy for the stream. This takes two parameters:

highWaterMark
size(chunk): A method containing a parameter chunk — this indicates the size to use for each chunk, in bytes.

注意 : You could define your own custom queuingStrategy , or use an instance of ByteLengthQueuingStrategy or CountQueuingStrategy for this object value. If no queuingStrategy is supplied, the default used is the same as a CountQueuingStrategy with a high water mark of 1.

返回值

An instance of the ReadableStream 对象。

异常

RangeError: The supplied type value is neither "bytes" nor undefined .

范例

In the following simple example, a custom ReadableStream is created using a constructor (see our Simple random stream example for the full code). The start() function generates a random string of text every second and enqueues it into the stream. A cancel() fuction is also provided to stop the generation if ReadableStream.cancel() is called for any reason.

When a button is pressed, the generation is stopped, the stream is closed using ReadableStreamDefaultController.close() , and another function is run, which reads the data back out of the stream.

const stream = new ReadableStream({
  start(controller) {
    interval = setInterval(() => {
      let string = randomChars();
      // Add the string to the stream
      controller.enqueue(string);
      // show it on the screen
      let listItem = document.createElement('li');
      listItem.textContent = string;
      list1.appendChild(listItem);
    }, 1000);
    button.addEventListener('click', function() {
      clearInterval(interval);
      fetchStream();
      controller.close();
    })
  },
  pull(controller) {
    // We don't really need a pull in this example
  },
  cancel() {
    // This is called if the reader cancels,
    // so we should stop generating strings
    clearInterval(interval);
  }
});

规范

规范	状态	注释
流 The definition of 'ReadableStream()' in that specification.	实时标准	初始定义。

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`ReadableStream()` 构造函数	Chrome 43	Edge 79	Firefox 65 65 57 Disabled Disabled From version 57: this feature is behind the `dom.streams.enabled` preference (needs to be set to `true` ) 和 preference (needs to be set to ). To change preferences in Firefox, visit about:config.	IE No	Opera 30	Safari 10.1	WebView Android 43	Chrome Android 43	Firefox Android 65 65 57 Disabled Disabled From version 57: this feature is behind the `dom.streams.enabled` preference (needs to be set to `true` ) 和 preference (needs to be set to ). To change preferences in Firefox, visit about:config.	Opera Android 30	Safari iOS 10.3	Samsung Internet Android 4.0

图例

完整支持
不支持
实验。期望将来行为有所改变。
用户必须明确启用此特征。

元数据

最后修改： Mar 6, 2020

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句法

参数

返回值

异常

范例

规范

浏览器兼容性

图例

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