JavaScript Reserved Words

Welcome to TheCodingCollege.com! In JavaScript, reserved words are terms that the language has predefined for specific purposes, such as keywords, future use, or global objects. Understanding these reserved words is essential to avoid syntax errors and write clean, functional code.

In this guide, we’ll cover:

• What reserved words are in JavaScript.
• Lists of reserved words for ES5 and ES6.
• Best practices for avoiding conflicts in your code.

What Are Reserved Words in JavaScript?

Reserved words in JavaScript are terms that you cannot use as:

• Variable names
• Function names
• Object property names (though technically allowed, it’s discouraged for clarity)

These words are either:

1. JavaScript Keywords: Used by the language to define actions, conditions, or structures.
2. Future Reserved Words: Reserved for potential future JavaScript enhancements.
3. Global Objects: Built-in objects that are always available, such as Math or Date.

List of JavaScript Reserved Words

1. JavaScript Keywords

These are part of the JavaScript language and serve specific functions.

Reserved Word	Purpose
break	Terminates a loop or switch statement.
case	Defines cases in a switch statement.
catch	Handles exceptions in try blocks.
class	Declares a class (ES6).
const	Declares a constant variable.
continue	Skips to the next iteration of a loop.
debugger	Pauses execution for debugging.
default	Defines the default case in switch.
delete	Deletes an object property.
do	Starts a do...while loop.
else	Defines the alternative block of an if statement.
export	Exports a module (ES6).
extends	Extends a class (ES6).
finally	Defines cleanup code after try...catch.
for	Declares a for loop.
function	Declares a function.
if	Starts a conditional statement.
import	Imports a module (ES6).
in	Checks if a property exists in an object.
instanceof	Checks if an object is an instance of a class.
let	Declares a block-scoped variable.
new	Creates an instance of an object.
return	Returns a value from a function.
super	Refers to the parent class (ES6).
switch	Starts a switch statement.
this	Refers to the current object.
throw	Throws an exception.
try	Defines a block of code to test for errors.
typeof	Returns the data type of a variable.
var	Declares a variable (function-scoped).
void	Evaluates an expression without returning a value.
while	Starts a while loop.
with	Extends the scope chain (deprecated).
yield	Pauses and resumes a generator function (ES6).

2. Future Reserved Words

These are reserved for potential future use in JavaScript and should be avoided as variable names.

Reserved Word	Notes
enum	Reserved for enums.
await	Reserved for async operations.

3. Global Objects

While not technically “reserved,” these are part of the JavaScript runtime and shouldn’t be overwritten.

Global Object	Purpose
Array	Represents an array.
Date	Represents date and time.
Math	Provides mathematical functions.
JSON	Handles JSON data.
Promise	Represents asynchronous operations.

Best Practices to Avoid Reserved Word Conflicts

1. Use Descriptive Names
   Always use meaningful variable and function names to avoid conflicts. // Avoid let class = 'Math'; // Error // Use let className = 'Math';
2. Follow Naming Conventions
   Use camelCase for variables and functions, and PascalCase for classes.
3. Lint Your Code
   Use tools like ESLint to detect potential issues with reserved words.
4. Keep Updated
   Stay informed about new ECMAScript features to avoid using newly reserved words.

Why Learn About Reserved Words with TheCodingCollege.com?

At TheCodingCollege.com, we aim to provide:

• Clear explanations of JavaScript concepts.
• Practical examples to help you avoid errors.
• Tutorials designed to improve your coding skills.

Understanding reserved words ensures your code is error-free and compatible across environments.

Conclusion

Reserved words in JavaScript play a critical role in defining the structure and functionality of the language. Avoiding their misuse ensures that your code is clean, maintainable, and free from syntax errors.