The ReadableStreamDefaultReader()
constructor creates and returns a ReadableStreamDefaultReader
object instance.
Note: You generally wouldn't use this constructor manually; instead, you'd use the ReadableStream.getReader()
method.
Syntax
var readableStreamDefaultReader = new ReadableStreamDefaultReader(stream);
Parameters
- stream
- The
ReadableStream
to be read.
Return value
An instance of the ReadableStreamDefaultReader
object.
Exceptions
- TypeError
- The supplied
stream
parameter is not aReadableStream
, or it is already locked for reading by another reader.
Examples
In the following simple example, a previously-created custom ReadableStream
is read using a ReadableStreamDefaultReader
created using getReader()
. (see our Simple random stream example for the full code). 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.
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"); 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); }); }
Specifications
Specification | Status | Comment |
---|---|---|
Streams The definition of 'ReadableStreamDefaultReader()' in that specification. |
Living Standard | Initial definition. |
Browser compatibility
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.
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
ReadableStreamDefaultReader() constructor | Chrome ? | Edge ? | Firefox
Full support
65
| IE ? | Opera ? | Safari ? | WebView Android ? | Chrome Android ? | Firefox Android
Full support
65
| Opera Android ? | Safari iOS ? | Samsung Internet Android ? |
Legend
- Full support
- Full support
- Compatibility unknown
- Compatibility unknown
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.
- User must explicitly enable this feature.
- User must explicitly enable this feature.