What is a Callback function in Node.js?

 Node.js, being an asynchronous platform, doesn’t wait around for things like file I/O to finish — Node.js uses callbacks. A callback is a function called at the completion of a given task; this prevents any blocking, and allows other code to be run in the meantime.

Image for post

Callbacks are the foundation of Node.js. Callbacks give us an interface with which to say, “and when you’re done doing that, do all this.” This allows us to have as many IO operations as our OS can handle happening at the same time. For example, in a web server with hundreds or thousands of pending requests with multiple blocking queries, performing the blocking queries asynchronously gives you the ability to be able to continue working and not just sit still and wait until the blocking operations come back.

Comments

Post a Comment

Popular posts from this blog

Which node logger did you use in your project?

Following are the common logger modules: 1) logger SUMMARY A simple logging library that combines the simple APIs of Ruby's logger.rb and browser-js console.log() USAGE A logger has 5 different levels of logging in a specific order: 'fatal', 'error', 'warn', 'info', 'debug' Each of these log levels has its own method on the logging instance. You can set the maximum log level on a logger at runtime. By default, a logger writes to STDOUT, but given a writeable file path, it will log directly to a file. Instantiation: // node/common.js style var logger = require('./logger').createLogger(); // logs to STDOUT var logger = require('./logger').createLogger('development.log'); // logs to a file 2)  simple-node-logger A simple multi-level logger for console, file, and rolling file appenders. Features include: levels: trace, debug, info, warn, error and fatal levels (plus all and off) flexible ap...
Read more

What is promise, promise.all and promise.race? How do you chain promises?

A promise is an object that may produce a single value some time in the future : either a resolved value, or a reason that it’s not resolved (e.g., a network error occurred). A promise is an object which can be returned synchronously from an asynchronous function. It will be in one of 3 possible states: Fulfilled:   onFulfilled()  will be called (e.g.,  resolve()  was called) Rejected:   onRejected()  will be called (e.g.,  reject()  was called) Pending:  not yet fulfilled or rejected A promise is  settled  if it’s not pending (it has been resolved or rejected). Sometimes people use  resolved  and  settled  to mean the same thing:  not pending . Once settled, a promise can not be resettled. Calling  resolve()  or  reject()  again will have no effect. The immutability of a settled promise is an important feature. Promises following the spec must follow a specific set of rules: A promise or...
Read more