JavaScript Default Parameters

Initialization:

• Default parameters allow initializing function parameters with default values if no argument or an undefined value is passed during function invocation.

Syntax:

• Default parameters are defined in the function declaration using the assignment operator (=) followed by the default value.

Example: Basic Usage

function greet(name = 'Guest') {
  console.log(`Hello, ${name}!`);
}
greet(); // Output: Hello, Guest!

Example: Default Parameter with Expression

function calculateArea(radius, pi = 3.14) {
  return pi * radius * radius;
}

Example: Default Parameters and Destructuring

function createUser({ username = 'guest', isAdmin = false } = {}) {
  // Function logic
}

No TDZ Issue:

• Default parameters do not create a Temporal Dead Zone (TDZ) and can reference variables declared before them in the parameter list.

Order of Parameters:

• Default parameters must be declared after non-default parameters in the function declaration.

Example: Order of Parameters

function example(a, b = 10, c) {
  // Valid declaration
}

 

Key Points

• Default parameters provide a convenient way to handle missing or undefined values in function parameters.
• They improve code readability and simplify function invocation by specifying default values directly in the function declaration.
• Default parameters are compatible with destructuring and can reference variables declared before them in the parameter list.