In Node.js, you can retrieve environment variables by key from process.env object.

node -p process.env
node -p process.env.HOME

References

• http://stackoverflow.com/questions/15058954/node-js-is-there-any-documentation-about-the-process-env-variable
• https://nodejs.org/api/process.html#process_process_env
• https://davidwalsh.name/node-environment-variables

Git blame helps in viewing the line by line revision history for an entire file.

References

• https://zsoltfabok.com/blog/2012/02/git-blame-line-history/
• https://help.github.com/articles/tracing-changes-in-a-file/
• https://git-scm.com/docs/git-blame

Declarative programming is more like what you do, or something. Imperative programming is like how you dome something. Declartive programming can be context-independent.

References

• https://tylermcginnis.com/imperative-vs-declarative-programming/

Factories are simply functions that create objects. You can use factories instead of classes, and factories are simpler than classes and easier to reason about.

References

• https://medium.com/humans-create-software/factory-functions-in-javascript-video-d38e49802555
• https://medium.com/javascript-scene/javascript-factory-functions-vs-constructor-functions-vs-classes-2f22ceddf33e
• https://www.sitepoint.com/factory-functions-javascript/

Destructuring assignment allows you to assign the properties of an array or object to variables using syntax that looks similar to array or object literals. This syntax can be extremely terse, while still exhibiting more clarity than the traditional property access. This new syntax was introduced in ECMAScript 2015 (ES6).

// Array destructuring
let arr = [1, 2, 3];
let [a, b, c] = arr;
console.log(a); // 1
console.log(b); // 2
console.log(c); // 3

// Object destructuring
let obj = {
    x: 1,
    y: 2
}

let {x, y} = obj;
console.log(x); //1
console.log(y); //2

References

• ES6 In Depth: Destructuring
• Destructuring assignment