ReadableStreamDefaultReader: ReadableStreamDefaultReader() constructor
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since May 2022.
Note: This feature is available in Web Workers.
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
new ReadableStreamDefaultReader(stream)
Parameters
stream-
The
ReadableStreamto be read.
Return value
An instance of the ReadableStreamDefaultReader object.
Exceptions
TypeError-
Thrown if the supplied
streamparameter 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 |
|---|
| Streams # ref-for-default-reader-constructor① |
Browser compatibility
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