node-guide/section-02-javascript/syntax.js

/******************************************************************************
 * VARIABLES
 */

/* Outdated syntax
var name = 'Ken';
var age = 57;
var hasHobbies = true;
*/

// Using let and const for variables
const uname = 'Ken';
let age = 57;
let hasHobbies = true; 

/******************************************************************************
 * FUNCTIONS
 */

// Basic structure and use of a function
function basicSummarizeUser(userName, userAge, userHasHobbies) {
    return ('Name is ' + userName + ', age is ' + userAge + ', and the user has hobbies: ' + userHasHobbies);
}
console.log(basicSummarizeUser(uname, age, hasHobbies));

// A named function
const namedSummarizeUser = function(userName, userAge, userHasHobbies) {
    return ('Name is ' + userName + ', age is ' + userAge + ', and the user has hobbies: ' + userHasHobbies);
}
console.log(namedSummarizeUser(uname, age, hasHobbies));

// Arrow function syntax: affects the use of 'this'
const arrowSummarizeUser = (userName, userAge, userHasHobbies) => {
    return ('Name is ' + userName + ', age is ' + userAge + ', and the user has hobbies: ' + userHasHobbies);
}
console.log(arrowSummarizeUser(uname, age, hasHobbies));

// Arrow function when there is a single statement in the function
const add = (a, b) => a + b;
console.log(add(1, 2));

/******************************************************************************
 * OBJECTS
 */

const person = {
    name: 'Ken',
    age: 57,

    greet() {
        console.log(`Hi I am ${name}`);
    }
}
console.log(person)

/******************************************************************************
 * ARRAYS
 */
const hobbies = ['Sports', 'Cooking'];
for(let hobby of hobbies) {
    console.log(hobby);
}

/******************************************************************************
 * SPREAD AND REST OPERATORS
 */

// Simply copying an array
const copiedArray = hobbies.slice();
console.log(copiedArray);

// Making a copy using SPREAD
const copiedAgainArray = [...hobbies];

// Can use SPREAD to copy objects too
const copiedPerson = {...person}

// REST bundles items together
const toArray = (...args) => {
    return args;
};
console.log(toArray(1, 2, 3, 4)); // The REST operator let's me hand in a variable number of arguments

/******************************************************************************
 * DESTRUCTURING
 */

const printName = (personData) => {
    console.log(personData.name);
}
printName(person);

// Alternative using destructuring

const printNameD = ({name}) => {
    console.log(name);
}
printNameD(person); // Still pass in the object but only the name prop is passed

/******************************************************************************
 * ASYNC CODE and PROMISES
 */

const fetchData = () => {
    const promise = new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Done');
        }, 1500);
    });
    return promise;
};

setTimeout(() => {
    console.log('Timer is done');
    fetchData().then(text => {
        console.log(text);
    });
}, 2000);