Unit 2, Lesson 4

$\textbf{Functions in Node.JS}$
$\text{Written by:} $
$\text{Dev Singh, Class of 2020}$
$\text{Last Revised: March 2020}$

Normal function structure

function sayGenericHello() {
    console.log("Hello!")
}

Note how the above function has no parameters

function sayHello(nameToGreet) {
    let memer = true
    console.log("Hello, " + nameToGreet)
    console.log(memer)
}

Note how the above function takes one parameter, and it's following behavior when it does not recieve that arguement.

sayHello()

Hello, undefined
true

sayHello("Stoodents")

Hello, Stoodents
true

Guiding Questions

How would I implement some sort of system where if the name is undefined, to replace it with "Unknown Person"?

What do you think would happen if I were to try to console.log() the value of memer outside of the function?

What was returned by sayHello(), if anything? How do you think I could define a return?

Anonymous Functions

let sayHello2 = function (nameToGreet) {
    console.log("Hello, " + nameToGreet)
}

sayHello2("Memer")

Hello, Memer

Arrow functions

As you may see, the syntax of defining functions in JS is somewhat ugly. A different syntax, arrow functions, have some cleaner syntax. Arrow functions were introduced in ECMAScript 6 and allow you to write cleaner code.

let sayHello3 = (nameToGreet) => { // the `let` is not technically neccessary.
    console.log("Hello, " + nameToGreet)
}
let sayHelloGeneric1 = () => { // the `let` is not technically neccessary.
    console.log("Hello!")
}

sayHello3("Person")

Hello, Person

sayHelloGeneric1()

Hello!

Topics we will go over in session

• async/await and the concept of promises
• Callbacks

Code snippet for analysis

(Yes, I stole this from my Robotics code)

let express = require("express")
let bodyParser = require("body-parser")
let dbHandler = require('./dbHandler.js')
let auth = require('./authHandler.js')
let expressMongoDb = require('express-mongo-db');
const port = process.env.PORT || 8190;

app = express()
app.use(bodyParser.json())
app.use(bodyParser.urlencoded({extended: true}))
let options = {
    keepAlive: 1, connectTimeoutMS: 30000
};
app.use(expressMongoDb('mongodb+srv://api-user-new:titanscout2022@2022-scouting-4vfuu.mongodb.net/test?retryWrites=true&w=majority', options))

/**
 * POST route "/api/submitMatchData"
 * Allows the application to submit data to the API, with some key data seperated within the JSON and the rest submitted as arbirtary structures within the data key.
 * @param token in form of header with title 'token' and value of JWT provided by Google OAuth
 * @param competition_id is the identifier for the competition: e.g. "2020ilch".
 * @param match_number is the number of the match scouted: e.g. "1".
 * @param team_scouted is the team that was being scouted: e.g. "3061".
 * @param data is the arbritrary other data that needs to be recorded for the match.
 * @returns back to the client resobj (success boolean, competition id, and match number) and HTTP Status Code 200 OK.
 */
app.post("/api/submitMatchData", auth.checkAuth, async (req, res) => {
    let val;
    const scouter = {name: String(res.locals.name), id: String(res.locals.id)}
    const competition_id = String(req.body.competition_id)
    const match_number = parseInt(req.body.match_number)
    const team_scouted = parseInt(req.body.team_scouted)
    const data = req.body.data
    try{
        val = await dbHandler.submitMatchData(req.db, scouter, competition_id, match_number, team_scouted, data).catch(e => {console.error(e); val.err_occur = true;})
    } catch (err) {
        console.error(err)
        val.err_occur = true;
    }
    if (val.err_occur == false) {
        resobj = {
            "success": true,
            "competition": competition_id,
            "match_number" : match_number,
        }
    } else {
        resobj = {
            "success": false,
            "reasons": val.err_reasons,
        }
    }
    res.json(resobj)
})