JavaScript Statement & Expression

JavaScript Keywords

JavaScript keywords are reserved words that have a special meaning in JavaScript.

These words are already used by JavaScript for specific tasks, so you cannot use them as variable names, function names, or object names.

Example

javascript

let name = "Amit";

Here, let is a JavaScript keyword. It is used to declare a variable.

What are Keywords?

Keywords are special words that JavaScript understands.

Each keyword has a fixed purpose.

Example

javascript

if (age >= 18) {
  console.log("You are eligible.");
}

In this example:

Keyword	Use
`if`	Checks a condition

The word if has a special meaning in JavaScript, so it cannot be used as a variable name.

Common JavaScript Keywords

Here are some commonly used JavaScript keywords:

Keyword	Use
`let`	Declares a variable
`const`	Declares a constant variable
`var`	Declares a variable
`if`	Starts a condition
`else`	Runs code when condition is false
`switch`	Checks multiple cases
`case`	Defines a case inside switch
`break`	Stops a loop or switch
`for`	Starts a for loop
`while`	Starts a while loop
`function`	Defines a function
`return`	Returns a value from a function
`class`	Defines a class
`new`	Creates a new object
`try`	Tests a block of code
`catch`	Handles errors
`import`	Imports code from another file
`export`	Exports code to another file

Keywords for Variables

JavaScript uses let, const, and var to declare variables.

Example

javascript

let userName = "Amit";
const country = "India";
var city = "Delhi";

In modern JavaScript, let and const are used more commonly than var.

Keywords for Conditions

JavaScript uses keywords like if, else, and switch for conditions.

Example

javascript

let age = 20;

if (age >= 18) {
  console.log("Adult");
} else {
  console.log("Minor");
}

Here, if checks the condition, and else runs when the condition is false.

Keywords for Loops

JavaScript uses keywords like for, while, and break with loops.

Example

javascript

for (let i = 1; i <= 3; i++) {
  console.log(i);
}

Here, for is used to repeat code.

The break keyword can stop a loop.

Example

javascript

for (let i = 1; i <= 5; i++) {
  if (i === 3) {
    break;
  }

  console.log(i);
}

Keywords for Functions

JavaScript uses function and return to create and use functions.

Example

javascript

function add(a, b) {
  return a + b;
}

let result = add(10, 20);

Here:

Keyword	Use
`function`	Creates a function
`return`	Sends a value back from the function

Keywords Cannot Be Used as Names

You cannot use JavaScript keywords as variable names.

Wrong example:

Wrong Example

javascript

let if = "Hello";
let function = "Test";
let return = 100;

These names are not allowed because if, function, and return are reserved keywords.

Correct example:

Correct Example

javascript

let userStatus = "Hello";
let functionName = "Test";
let returnValue = 100;

Use meaningful names that are not JavaScript keywords.

Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Keywords</title>
</head>
<body>

  <h1>JavaScript Keywords</h1>

  <p id="result"></p>

  <script>
    let age = 20;
    let message;

    if (age >= 18) {
      message = "You are eligible.";
    } else {
      message = "You are not eligible.";
    }

    document.getElementById("result").innerHTML = message;
  </script>

</body>
</html>

Try It Yourself

Run the above example in the Try It Editor.

Try changing the value of age and check how the result changes.

Also try using different keywords like const, function, and return.

Important Points

JavaScript keywords are reserved words.
Each keyword has a special meaning.
Keywords cannot be used as variable names.
Common keywords include let, const, if, else, for, while, function, and return.
Use meaningful names for variables and functions instead of reserved keywords.

Conclusion

JavaScript keywords are special reserved words used to perform specific tasks.

They help JavaScript create variables, check conditions, run loops, define functions, handle errors, and work with modules.

Understanding keywords is important because they are used in almost every JavaScript program.

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