**Course Title:** Modern JavaScript Programming: From Fundamentals to Full-Stack Development **Section Title:** Introduction to JavaScript and Setup **Topic:** Basic syntax: Variables (var, let, const), data types, operators, and expressions. As we've covered the history and setup of JavaScript in our previous topics, it's now time to dive into the language's basic syntax. This topic is crucial for building a strong foundation in JavaScript programming. In this section, we'll explore variables, data types, operators, and expressions. ### Variables In JavaScript, a variable is a container used to store a value. You can think of it as a labeled box where you can store and retrieve values. JavaScript has three types of variables: `var`, `let`, and `const`. Each has its own scope and usage. * **`var`**: This is the oldest way of declaring variables in JavaScript. It has a global scope, which means it can be accessed from anywhere in the code. However, it can also lead to issues with variable hoisting and scope pollution. Example: ```javascript var name = 'John Doe'; console.log(name); // Output: John Doe ``` * **`let`**: Introduced in ECMAScript 2015 (ES6), `let` has a block scope, which means it's limited to the block it's declared in. It's the recommended way to declare variables in modern JavaScript. Example: ```javascript let name = 'John Doe'; console.log(name); // Output: John Doe ``` * **`const`**: This is used to declare constants, which cannot be changed once declared. Like `let`, `const` has a block scope. Example: ```javascript const PI = 3.14; console.log(PI); // Output: 3.14 try { PI = 2.71; console.log(PI); } catch (error) { console.log('Error: Cannot reassign a constant.'); } ``` ### Data Types JavaScript is a dynamically typed language, which means you don't need to specify the data type when declaring a variable. There are six primitive data types in JavaScript: * **Number**: This includes integers, floating-point numbers, and NaN (Not a Number). Example: `let age = 25;` * **String**: This includes text values, which can be enclosed in single quotes or double quotes. Example: `let name = 'John Doe';` * **Boolean**: This represents a true or false value. Example: `let isAdmin = true;` * **Null**: This represents the absence of a value. Example: `let favoriteColor = null;` * **Undefined**: This represents an uninitialized variable. Example: `let favoriteFood; console.log(favoriteFood); // Output: undefined` * **Symbol**: This is a unique identifier, introduced in ECMAScript 2015 (ES6). Example: `let uniqueId = Symbol('uniqueId');` ### Operators Operators are used to perform operations on variables and values. Here are some common operators: * **Arithmetic Operators**: + `+` (addition) + `-` (subtraction) + `*` (multiplication) + `/` (division) + `%` (modulus) + `**` (exponentiation) * **Assignment Operators**: + `=` (assignment) + `+=` (addition assignment) + `-=` (subtraction assignment) + `*=` (multiplication assignment) + `/=` (division assignment) + `%=` (modulus assignment) + `**=` (exponentiation assignment) * **Comparison Operators**: + `===` (strict equality) + `!==` (strict inequality) + `==` (loose equality) + `!=` (loose inequality) + `>` (greater than) + `<` (less than) + `>=` (greater than or equal to) + `<=` (less than or equal to) * **Logical Operators**: + `&&` (logical and) + `||` (logical or) + `!` (logical not) ### Expressions Expressions are combinations of variables, operators, and values that evaluate to a value. For example: * `2 + 2` (expression evaluates to 4) * `5 * 5` (expression evaluates to 25) * `let name = 'John Doe'; name + ' is a developer.'` (expression evaluates to 'John Doe is a developer.') You can also use parentheses to group expressions and control the order of operations. * `(2 + 2) * 3` (expression evaluates to 12) MDN Web Docs has an exhaustive list of [operators](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators) and [expressions](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#Expressions) in JavaScript. **Practical Takeaways:** * Always use `let` and `const` instead of `var` for variable declarations. * Use `const` for variables that don't change value. * Use template literals for string expressions, introduced in ECMAScript 2015 (ES6). * Use the `**` operator for exponentiation instead of `Math.pow()`. If you have any questions or need help with understanding these concepts, feel free to ask in the comments below. In the next topic, we'll cover running JavaScript in the browser console and via Node.js. **What's next?** Next, we'll explore how to run JavaScript in the browser console and via Node.js. This will give you hands-on experience with executing JavaScript code and observing the results.