TypeScript

Intro:

1. Superset of JavaScript.
2. Object-oriented and tightly typed programming language.
3. TypeScript code is transformed to JavaScript, which may be used in any environment that supports JavaScript,
4. This including browsers, Node.js, and your own applications.

Array in TypeScript

Using square brackets ([]):

let numbers: number[] = [1, 2, 3, 4, 5];
let strings: string[] = ['a', 'b', 'c'];

Using the Array generic type:

let numbers: Array<number> = [1, 2, 3, 4, 5];
let strings: Array<string> = ['a', 'b', 'c'];

Mixed array types:

let mixed: (number | string)[] = [1, 'two', 3, 'four'];

Using a tuple (fixed length and types):

let tuple: [number, string, boolean] = [1, 'hello', true];

Disadvantages of TypeScript

1. It takes a long time to compile TypeScript code.
2. Abstract classes are not supported in TypeScript.
3. Converting TypeScript to JavaScript requires an additional compilation step.
4. Its type scheme is extremely complicated.

never and any
Key Differences
never:

Used for functions that do not return.
Represents a value that never occurs.
Useful for exhaustive type checking.
any:

Disables type checking for a variable.
Can hold any type of value.
Useful for migrating JavaScript to TypeScript or working with dynamic data

Tuples

// define our tuple
let ourTuple: [number, boolean, string];

// initialized incorrectly which throws an error
ourTuple = [false, 'Coding God was mistaken', 5];

// define our tuple
let ourTuple: [number, boolean, string];
// initialize correctly
ourTuple = [5, false, 'Coding God was here'];
// We have no type safety in our tuple for indexes 3+
ourTuple.push('Something new and wrong');
console.log(ourTuple);

New valueTuples only have strongly defined types for the initial values:

// define our readonly tuple
const ourReadonlyTuple: readonly [number, boolean, string] = [5, true, 'The Real Coding God'];
// throws error as it is readonly.
ourReadonlyTuple.push('Coding God took a day off');

Function

// the `: number` here specifies that this function returns a number
function getTime(): number {
  return new Date().getTime();
}

Optional Parameter

// the `?` operator here marks parameter `c` as optional
function add(a: number, b: number, c?: number) {
  return a + b + (c || 0);
}

Default Parameters

function pow(value: number, exponent: number = 10) {
  return value ** exponent;
}

Object as an argument

function divide({ dividend, divisor }: { dividend: number, divisor: number }) {
  return dividend / divisor;
}

Rest Paramter

function add(a: number, b: number, ...rest: number[]) {
  return a + b + rest.reduce((p, c) => p + c, 0);
}