JavaScript

Sample repo with JavaScript samples and sandbox project. For details see individual project README files.

Learning Fundamentals

JavaScript Fundamentals from Mark Zamoyta course on Pluralsight.

Language Features

Constants

const carId = 42;

Variables

You can either use var or let. The difference is that let has scoping, which means you can't use the variable outside the scope it is defined in.

// you can only use the variable after it was defined
// console.log(carId);
let carId = 42;

// you can use the variable before to get `undefined` value
console.log(carId); // undefined
var carId = 42; 

Rest Parameters

function sendCars(day, ...allCarIds) {
  allCarIds.forEach( id => console.log(id));
}

sendCars('Monday', 100, 200, 555);

Destructuring

Desctructuring arrays example:

let carIds = [1, 2, 5];
let car1, remainingCars;
[car1, ... remainingCars] = carIds;

console.log(car1, remainingCars);

Destructuring objects example:

let car = { id: 5000, style: 'convertible' };
let {id, style} = car;

console.log(id, style);

Spread Syntax

The oposite to destructuring is spreading:

function startCars(car1, car2, car3) {
  console.log(car1, car2, car3);
}

let carIds = [100, 30, 500];
startCars(...carIds); // 100 30 500

let carCodes = 'abc';
startCars(...carCodes); // a b c

TypeOf

Returns type of a variable, constant or a literal value:

• typeof(1): number
• typeof(true): boolean
• typeof('Hello'): string
• typeof( function() {}): function
• typeof({}): object
• typeof(null): object
• typeof(undefined): undefined
• typeof(NaN): number

Common Type Conversion

// convert to string
foo.toString();

// convert string to integer
Number.parseInt('55'); // 55 as a number

// convert string to number
Number.parseFloat('55.99'); // 55.99 as a number

Controlling Loops

Simple for loops:

for (let i=0; i<4; i++) {
  if (i === 2) {
    continue;
  }

  console.log(i);
}

Operators

Equality Operators

• var1 == var2: it will do the necessary conversion before doing the comparison
• var1 === var2: it will only compare values (no conversion is done)

Similarly for inequality, != and !==.

console.log(1 == 1); // true
console.log(1 == true); // true
console.log(1 === true); // false

Unary Operators

Same as any other language, like i++, ++i, -i, etc.

Logical (Boolean) Operators

• &&: logical AND operator
• ||: logical OR operator

Relational Operators

Same as any other language, like <, <=, etc.

Conditional Operator

Same as any other language, (condition ? then : else).

Assignment Operator

Same as any other language, like +=, -=, /=, etc.

Operator Precedence

See Mozilla documentation for table with operator precedence.

Functions and Scopes

IIFE Pattern

IIFE stands for Immediately Invoked Function Expression.

// just function
function() {
  console.log('in function');
}

  // iife - executed immediately
(function() {
  console.log('in function');
})();

Closures

let app = (function() {
  let carId = 123;
  let getId = function() {
    return carId;
  };
  return {
    getId: getId
  };
})();
console.log(app.getId());