Home Reference Source 
import EventQueue from 'jseventqueue'
public class | source

EventQueue

Event queue with support for async-await reading by a single consumer

Constructor Summary

Public Constructor
public

Default constructor

Member Summary

Public Members
public get

end: *

Getter for the end marker.

Method Summary

Public Methods
public

Support for for-await-of loop
public

isSignal(signal: *): *

Checks whether an object was created by raiseSginal method.
public

Send a message containing an Error object.
public

async receive(): *

Async method that can be waited on to receive the next message.
public

send(val: *)

Sends a message to a waiting consumer, or stores it in-memory to be delivered later.
public

Closes queue from accepting more messages for delivery

Public Constructors

public constructor() source

Default constructor

Public Members

public get end: * source

Getter for the end marker. This object is sent when queue is shutdown

Public Methods

public [Symbol.asyncIterator](): * source

Support for for-await-of loop

Return:

*

public isSignal(signal: *): * source

Checks whether an object was created by raiseSginal method.

Params:

NameTypeAttributeDescription
signal *

Return:

*

public raiseSignal(err: Error) source

Send a message containing an Error object. Iterator will throw an exception when processing this object

Params:

NameTypeAttributeDescription
err Error

an error to be thrown

Example:

// Reading from queue using `for await` loop:
let queue = new EventQueue();
setTimeout(() => {
    queue.send(0);
    queue.send(1);
    queue.send(2);
    queue.raiseSignal(new Error('Processing failed'));
    queue.send(3);
    queue.shutdown();
}, 15);
let results = [];
try {
    for await (let data of queue) {
        results.push(data);
    }
}
catch(err) {
    // err.message is 'Processing failed'
}
// results contain [0, 1, 2]
// If for some reason one can't use `for await` loop then a similar loop can be implemented using `while`:
let queue = new EventQueue();
setTimeout(() => {
    queue.send(0);
    queue.send(1);
    queue.send(2);
    queue.raiseSignal(new Error('Processing failed'));
    queue.send(3);
    queue.shutdown();
}, 15);
let results = [];
let data;
// while loop checks whether queue was shutdown by comparing returned value
// to a special data member of the queue object. It also checks for signals and throws errors
try {
    while ((data = await queue.receive()) !== queue.end) {
        if (queue.isSignal(res)) {
            throw res.error;
        }
        results.push(data);
    }
}
finally {
}
// results contain [0, 1, 2, 3]

public async receive(): * source

Async method that can be waited on to receive the next message. At most one consumer at a time is expected to be waiting. The method throws an exception after queue was shut down and all pendingmessages were delivered.

Return:

*

public send(val: *) source

Sends a message to a waiting consumer, or stores it in-memory to be delivered later. Once the queue is shut down, no more messages are accepted for delivery. Pending messages will be delivered to a consumer.

Params:

NameTypeAttributeDescription
val *

value to be delivered

public shutdown() source

Closes queue from accepting more messages for delivery