JavaScript Fundamentals: Data Types, Variables, Operators, Control Statements, Loops, Functions, and In-Built Methods By Shivam Maurya

 

1. Data Types:

Primitive Data Types:

• String: Represents a sequence of characters, enclosed in single (') or double (") quotes.

  javascript
  let greeting = "Hello, World!";
  

• Number: Represents numeric values.

  javascript
  let age = 25;
  

• Boolean: Represents either true or false.

  javascript
  let isStudent = true;
  

• Undefined: Represents an uninitialized variable. If a variable is declared but not assigned a value, it is undefined.

  javascript
  let notDefined;
  

• Null: Represents the intentional absence of any object value.

  javascript
  let noValue = null;
  

Non-Primitive Data Types:

• Object: Represents a collection of key-value pairs.

  javascript
  let person = {
    name: "John",
    age: 30,
    isStudent: false
  };

• Array: Represents an ordered list of values.

  javascript
  let fruits = ["apple", "banana", "orange"];
  

• Function: Represents a reusable block of code.

  javascript
  function greet(name) {
    console.log("Hello, " + name + "!");
  }

2. Variables:

Variables are used to store values. In JavaScript, you can declare variables using var, let, or const.

• var (function-scoped): The original way to declare variables.
• let (block-scoped): Introduced in ES6, allows reassignment.
• const (block-scoped): Declares a variable with a constant value.

javascript
var myVar = "Hello";
let myNumber = 42;
const pi = 3.14;

3. Operators:

• Arithmetic Operators: Perform mathematical operations.

  javascript
  let a = 5;
  let b = 2;
  console.log(a + b); // Addition: 7

• Comparison Operators: Compare values and return a boolean result.

  javascript
  let x = 10;
  let y = 5;
  console.log(x > y); // Greater than: true

• Logical Operators: Perform logical operations.

  javascript
  let isTrue = true;
  let isFalse = false;
  console.log(isTrue && isFalse); // Logical AND: false

4. Control Conditional Statements:

• if Statement: Executes a block of code if a specified condition is true.

  javascript
  let num = 10;
  if (num > 0) {
    console.log("Number is positive");
  }

• if...else Statement: Executes one block of code if the condition is true, and another if it's false.

  javascript
  let num = -5;
  if (num > 0) {
    console.log("Number is positive");
  } else {
    console.log("Number is non-positive");
  }

• nested if...else Statement: Uses multiple if...else statements for complex conditions.

  javascript
  let num = 0;
  if (num > 0) {
    console.log("Number is positive");
  } else if (num < 0) {
    console.log("Number is negative");
  } else {
    console.log("Number is zero");
  }

• switch...case Statement: A switch statement allows a program to evaluate an expression and attempt to match the expression's value to a case label.

  javascript
  let day = "Monday";
  switch (day) {
    case "Monday":
      console.log("It's the start of the week");
      break;
    case "Friday":
      console.log("It's almost the weekend");
      break;
    default:
      console.log("It's a regular day");
  }

5. Loops:

• for Loop: Executes a block of code a specified number of times.

  javascript
  for (let i = 0; i < 5; i++) {
    console.log(i);
  }

• while Loop: Executes a block of code as long as a specified condition is true.

  javascript
  let i = 0;
  while (i < 5) {
    console.log(i);
    i++;
  }

6. Functions and Arrow Functions:

• Function Declaration: Defines a function using the function keyword.

  javascript
  function greet(name) {
    console.log("Hello, " + name + "!");
  }
  greet("John");

• Arrow Function: A concise way to define functions introduced in ES6.

  javascript
  const greet = (name) => {
    console.log(`Hello, ${name}!`);
  };
  greet("John");

7. In-built Methods and Properties:

• length: Returns the length of a string or the number of elements in an array.

  javascript
  let str = "Hello, World!";
  console.log(str.length); // Output: 13

• typeof: Returns a string representing the type of a variable.

  javascript
  let num = 42;
  console.log(typeof num); // Output: "number"

• join(): Joins all elements of an array into a string.

  javascript
  let arr = ["apple", "banana", "orange"];
  let joinedStr = arr.join(", ");
  console.log(joinedStr); // Output: "apple, banana, orange"