TypeScript Cheat Sheet

Hello World:

        
console.log("Hello, World!");
        
    

Variables:

        
// Declaring variables
let age: number;
let pi: number;
let name: string;

// Assigning values
age = 25;
pi = 3.14159;
name = "John Smith";

// Initializing variables
let count: number = 0;
let isTrue: boolean = true;
        
    

Data Types:

        
// Basic data types
let number: number;
let text: string;
let boolean: boolean;
let nullValue: null;
let undefinedValue: undefined;

// Array data type
let numbers: number[];
let texts: string[];
let booleans: boolean[];

// Object data type
let person: { name: string, age: number };

// Custom type
type MyType = {
    field1: string;
    field2: number;
};

let myObject: MyType;
        
    

Operators:

        
// Arithmetic operators
let sum: number = 5 + 3;
let difference: number = 10 - 4;
let division: number = 15 / 2;
let remainder: number = 15 % 2;
let product: number = 4 * 6;

// Comparison operators
let isEqual: boolean = (5 === 5);
let isGreater: boolean = (10 > 5);
let isLessThanOrEqual: boolean = (15 <= 20);

// Logical operators
let logicalAnd: boolean = true && false;
let logicalOr: boolean = true || false;
let logicalNot: boolean = !true;
        
    

Conditional Statements:

        
// If statement
if (condition) {
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}

// Switch statement
let day: number = 3;
switch (day) {
    case 1:
        console.log("Monday");
        break;
    case 2:
        console.log("Tuesday");
        break;
    case 3:
        console.log("Wednesday");
        break;
    default:
        console.log("Invalid day");
        break;
}
        
    

Loops:

        
// For loop
for (let i: number = 0; i < 5; i++) {
    // Code to execute repeatedly
}

// While loop
while (condition) {
    // Code to execute while the condition is true
}

// Do...while loop
do {
    // Code to execute at least once
} while (condition);

// For...in loop
let object = {
    key1: value1,
    key2: value2
};
for (let key in object) {
    console.log(key + ": " + object[key]);
}

// For...of loop
let array = [1, 2, 3, 4, 5];
for (let element of array) {
    console.log(element);
}
        
    

Functions:

        
// Function declaration
function functionName(parameters: type): returnType {
    // Code to execute
    return value;
}

// Function expression
let multiply = function(a: number, b: number): number {
    let result: number = a * b;
    return result;
};

// Arrow function
let divide = (a: number, b: number): number => {
    let result: number = a / b;
    return result;
};

// Optional and default parameters
function greet(name: string, greeting?: string = "Hello") {
    console.log(greeting + ", " + name);
}

// Function call
functionName(arguments);
        
    

Classes:

        
class MyClass {
    property: number;

    constructor(property: number) {
        this.property = property;
    }

    method() {
        console.log("Value: " + this.property);
    }
}

let myObject = new MyClass(10);
myObject.method();