node.md

node.js

Overview

node.js is a runtime, but is commonly mistaken for its own language. In reality it is a runtime that packages Chrome's v8 engine to execute javascript code. It provides additional modules to interact with the os and file system that it is running on. The motivation for creating node comes from the desire to have javascript powering both the frontend and backend of an application.

Foundational Knowledge

Every file in node is a module. To get metadata about the current module:

console.log(module);

All vars and functions are private and scoped to the module they are defined in. To use outside of the module these vars and functions must be explicitly exported:

function logger(msg){
    console.log(msg);
}
module.exports.log=logger;
// OR
exports.log=logger;

The exports object can then be set to a constant in another module:

const logger = require('/logger');

The logger function could then be called:

logger.log('Hello World!');

Single and double quotes are equal, but when converted to JSON everything is double.

CLI node args are available via process.argv. The first two elements are boiler plate so be sure to skip these.

__filename and __dirname are available in the module.

Sample template string:

var test = 'World';
console.log(`Hello ${test}`);

JavaScript Promises

Prior to Promises there was exclusively callbacks. With callbacks you would make a request to an API, let's say, and when the API would return there would be a callback function that would be called. With this structure you could easily get caught in a chain of nested callbacks.

Then along came promises, which are actually JS objects. Promises have states: pending, fulfilled and rejected. There are two main methods used to react to a change in promise state:

promise.then() - runs perscribed code when the corresponding promise is fulfilled.

promise.catch() - runs perscribed code whtn the corresponding promise is rejected.

It is worth noting that when chaining promises together, only one catch method is needed and it will catch any rejection in the chain.

JavaScript Objects

Javascript object attributes and functions can be accessed via dot notation or array index notation (square brackets). However, if you are accessing an object attribute/function using a variable you must use array index notation:

var test = 'hello';
var obj = {
    hello: 'world'
}
console.log(obj[test]);
console.log(obj.test); //UNDEFINED

Dynamic keys can also be used by leveraging array index notation:

var test = 'hello'
var obj = {
    [test]: 'World'
}