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StderrLineTransform class

This API is provided as a preview for developers and may change based on feedback that we receive. Do not use this API in a production environment.

StderrLineTransform normalizes lines that mix characters from stdout and stderr, so that each output line is routed entirely to stdout or stderr.


export declare class StderrLineTransform extends TerminalTransform 

Extends: TerminalTransform


IMPORTANT: This transform assumes that its input has been normalized to use "\n" newlines.

IMPORTANT: This transform does not produce realtime output, because lines are buffered until a newline character is encountered.

Suppose that a poorly behaved process produces output like this:

process.stderr.write('An error occurred, cleaning up');
process.stdout.write('.'); // (delay)
process.stdout.write('.'); // (delay)
process.stderr.write('The process completed with errors\n');

When stdout and stderr are combined on the console, the mistake in the output would not be noticeable:

An error occurred, cleaning up...
The process completed with errors

However, if we discard stdout, then stderr is malformed:

An error occurred, cleaning upThe process completed with errors

Tooling scripts can introduce these sorts of problems via edge cases that are difficult to find and fix.

StderrLineTransform normalizes the output so that if a combined line contains any stderr characters, then the entire line is routed to stderr. Later, if we discard stdout, then the output will preserve the appropriate context:

An error occurred, cleaning up...
The process completed with errors


Constructor Modifiers Description
(constructor)(options)   (BETA) Constructs a new instance of the StderrLineTransform class


Property Modifiers Type Description
newline   string (BETA)


Method Modifiers Description
onClose()   (BETA)
onWriteChunk(chunk)   (BETA)