Node.js Asynchronous Programming with Callbacks and Error Handling, Essays (university) of Software Project Management

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Node Modules: Callbacks and Error

Handling

Jogesh K. Muppala

Two Salient Features of JavaScript

• First-class functions: A function can be treated the

same way as any other variable

• Closures:

– A function defined inside another function has access to all

the variables declared in the outer function (outer scope)

– The inner function will continue to have access to the

variables from the outer scope even after the outer

function has returned

Node, Async I/O and Callbacks

Event Loop (single thread) requests File/ Database/ Processing I/O request Callback I/O request completion

Event Loop

timers I/O callbacks idle, prepare poll check close callbacks incoming: connections, data, etc.

• timers : this phase executes callbacks scheduled by setTimeout() and setInterval().
• I/O callbacks : executes almost all callbacks with the exception of close callbacks, the ones scheduled by timers, and setImmediate().
• idle, prepare : only used internally.
• poll : retrieve new I/O events; node will block here when appropriate.
• check : setImmediate() callbacks are invoked here.
• close callbacks : e.g. socket.on('close', ...).