Javascript-Datatypes,Variables, Operators,Conditional statement ,Looping-Tasks

JavaScript Fundamentals: Data Types, Variables, Operators, and Control Flow

This document provides a concise overview of fundamental JavaScript concepts, including data types, variables, operators, and control flow structures.

Data Types:

Data types classify the kind of values a variable can hold. JavaScript's eight primary data types enable efficient data handling and processing.

1. String: Represents textual data (e.g., "Hello").
2. Number: Represents numerical data (e.g., 10, 3.14).
3. BigInt: Represents arbitrarily large integers.
4. Boolean: Represents truth values (true or false).
5. Undefined: Indicates a variable has been declared but not assigned a value.
6. Null: Represents the intentional absence of a value.
7. Symbol: Creates unique and immutable values.
8. Object: Represents complex data structures.

Variables:

Variables are named storage locations for values. JavaScript offers several ways to declare variables:

• Automatic Declaration: x = 5; (Implicit declaration, generally discouraged for clarity).
• var: var x = 5; (Function-scoped, older style, use sparingly).
• let: let x = 5; (Block-scoped, allows reassignment).
• const: const x = 5; (Block-scoped, prevents reassignment after initialization; ideal for constants).

Choosing var, let, or const:

1. Always declare variables explicitly. Avoid implicit declarations.
2. Prefer const: Use const unless the value needs to change. This includes arrays and objects (their contents can be modified, but the variable itself cannot be reassigned).
3. Use let only when necessary: Employ let only when const is inappropriate due to the need for reassignment.
4. Avoid var in modern JavaScript: var has function scope, which can lead to unexpected behavior. Reserve it only for compatibility with very old browsers.

Operators:

JavaScript operators perform various computations. The following image provides a visual representation of common operators:

Conditional Statements:

Conditional statements control the flow of execution based on conditions.

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

   if (hour < 12) {
       console.log("Good morning");
   }

• else: Executes a block of code if the preceding if condition is false.

   if (hour < 12) {
       console.log("Good morning");
   } else {
       console.log("Good afternoon");
   }

• else if: Tests additional conditions if the preceding if and else if conditions are false.

   if (time < 10) {
       console.log("Good morning");
   } else if (time < 20) {
       console.log("Good day");
   } else {
       console.log("Good evening");
   }

• switch: (Not detailed here, but provides a concise way to handle multiple conditions).

Loops:

Loops repeatedly execute code blocks while a condition remains true.

1. while Loop:

The while loop continues as long as a specified condition is true.

Examples:

// Output: 5 4 3 2 1
let no = 5;
while (no > 0) {
  console.log(no);
  no--;
}

// Output: 1 2 3 4 5
let no = 1;
while (no <= 5) {
  console.log(no);
  no++;
}

// Output: 0 2 4 6 8 10
let no = 0;
while (no <= 10) {
  console.log(no);
  no += 2;
}

// Output: 10 8 6 4 2 0
let no = 10;
while (no >= 0) {
  console.log(no);
  no -= 2;
}

This revised response provides a more structured and comprehensive explanation of the provided JavaScript concepts. The code examples are also improved for clarity and accuracy.

The above is the detailed content of Javascript-Datatypes,Variables, Operators,Conditional statement ,Looping-Tasks. For more information, please follow other related articles on the PHP Chinese website!