Writer
Direct Subclass:
A writer is used to output a value through the Handler.
The output is determined by the kind of value that's passed to the writer where exceptions are interpreted as error output otherwise, the value is interpreted as success value. Therefore, new implements are expected to implement both a success (Writer._successOutput) and error (Writer._errorOutput) outputs.
Options: Custom options can be assigned to writers (Writer.setOption). They are passed from the handler to the writer during the output process (Handler.output).
const myHandler = Mebo.Handler.create('someHandler');
// setting output options during the output
myHandler.output(value, {
someOption: 10,
});
When an action is executed through a handler it can define options for readers and writers via Metadata support.
Options Summary
| Option Name | Description | Default Value |
|---|---|---|
| convertBufferToReadableStream | Tells if a buffer value should be converted to a readable stream |  |
| result | Overrides the value returned by Writer.value to an arbitrary value (only affects the success output) |  |
Constructor Summary
| Public Constructor | ||
| public |
constructor(value: *) Creates a writer |
|
Method Summary
| Public Methods | ||
| public |
Returns an option |
|
| public |
Serializes a writer value (Writer.value) in case the value is an exception it's serialize as Writer._errorOutput otherwise it's serialized as Writer._successOutput. |
|
| public |
Sets a value under the options |
|
| public |
value(): * Returns the value that should be serialized (Writer.serialize) by the writer. |
|
| Protected Methods | ||
| protected |
Translates an Error to a data structure that is later serialized by a writer implementation as output. |
|
| protected |
_successOutput(): Object | Stream Translates the success value to a data structure that is later serialized by a handler implementation as output. |
|
Public Constructors
public constructor(value: *) source
Creates a writer
Params:
| Name | Type | Attribute | Description |
| value | * | arbitrary value passed to the writer |
Public Methods
public option(path: string, defaultValue: *): * source
Returns an option
Params:
| Name | Type | Attribute | Description |
| path | string | path about where the option is localized (the levels must be separated by '.'). In case of an empty string it returns the entire options |
|
| defaultValue | * |
|
default value returned in case a value was not found for the path |
Return:
| * |
public serialize() source
Serializes a writer value (Writer.value) in case the value is an exception it's serialize as Writer._errorOutput otherwise it's serialized as Writer._successOutput.
public setOption(path: string, value: *, merge: boolean) source
Sets a value under the options
Params:
| Name | Type | Attribute | Description |
| path | string | path about where the option should be stored under the options (the levels must be separated by '.') |
|
| value | * | value that is going to be stored under the collection |
|
| merge | boolean |
|
this option is used to decide in case of the last level is already existing under the collection, if the value should be either merged (default) or overridden. |
public value(): * source
Returns the value that should be serialized (Writer.serialize) by the writer.
Return:
| * |
Protected Methods
protected _errorOutput(): Object source
Translates an Error to a data structure that is later serialized by a writer implementation as output. This method gets triggered when an exception is passed as value by the Handler.output.
By default the contents of the error output are driven by the err.message,
however if an error contains err.toJSON property (ValidationFail.toJSON)
then that's used instead of the message.
Also, you can avoid specific errors to be handled via output process by defining the member
output assigned with false to the error (for instance err.output = false;). If
that is in place the error gets thrown which triggers the event Handler.onErrorDuringOutput.
Tip: You can set the env variable NODE_ENV=development to get the traceback information
included in the error output
protected _successOutput(): Object | Stream source
Translates the success value to a data structure that is later serialized by a handler implementation as output.
/todo: This value is either driven by the option 'result' (when defined) or by the value defined at constructor time.
All writers shipped with Mebo have support for streams where in case of any readable stream or buffer value are piped to the output, otherwise the result is encoded using JSON (defined per writer bases).
Note: any Buffer value passed to this method gets automatically converted to a readable stream (this behavior is driven by the option 'convertBufferToReadableStream').
This method is called by Handler.output.