The adopt() method of DisposableStack instances registers a value that doesn't implement the disposable protocol to the stack by providing a custom disposer function.

Syntax

adopt(value, onDispose)

Parameters

value

Any value to be registered to the stack.

onDispose

A function that will be called when the stack is disposed. The function receives value as its only argument.

Return value

The same value that was passed in.

Exceptions

TypeError

Thrown if onDispose is not a function.

ReferenceError

Thrown if the stack is already disposed.

Description

The primary purpose of adopt() is to register a value that doesn't implement the disposable protocol to the stack. If the value is already disposable, you can use use() instead, which automatically uses the value's [Symbol.dispose]() method as the disposer.

adopt(value, onDispose) is almost the same as defer(() => onDispose(value)), but it allows you to declare the resource and register it on the same line. This way, there's minimal chance of an error happening between the resource creation and registration, which will cause the resource to leak.

using disposer = new DisposableStack();
const reader = disposer.adopt(stream.getReader(), (reader) =>
  reader.releaseLock(),
);

using disposer = new DisposableStack();
const reader = stream.getReader();
// If someone adds code in between these lines and an error occurs,
// the stream will be locked forever.
disposer.defer(() => reader.close());

In the same spirit of "make your resource registered as soon as it's declared", you should always wrap your resource acquisition expression in adopt(), instead of extracting it to a separate statement.

using disposer = new DisposableStack();
const reader = stream.getReader();
disposer.adopt(reader, (reader) => reader.close());

Examples

Using adopt()

This code consumes a ReadableStream via a ReadableStreamDefaultReader. The reader does not implement the disposable protocol, so we use adopt() to register it to the stack.

{
  using disposer = new DisposableStack();
  const reader = disposer.adopt(stream.getReader(), (reader) =>
    reader.releaseLock(),
  );
  const { value, done } = reader.read();
  if (!done) {
    // Process the value
  }
  // The reader.releaseLock() method is called here before exiting
}

Specifications

Browser compatibility

See also

• JavaScript resource management
• DisposableStack
• DisposableStack.prototype.defer()
• DisposableStack.prototype.use()