45. Default Parameters

Before ES6, handling missing parameters required manual checks inside the function body. Default parameters allow you to assign a default value to a parameter directly in the function definition, used only if the argument is omitted or is undefined.

Syntax

javascript function functionName(param1, param2 = defaultValue) { // ... }

Example: Setting Default User Role

javascript function createUser(name, role = 'standard') { console.log(User: ${name}, Role: ${role}); }

// Case 1: Argument provided createUser('Administrator', 'admin'); // User: Administrator, Role: admin

// Case 2: Argument omitted (uses default) createUser('Guest'); // User: Guest, Role: standard

// Case 3: Argument is explicit undefined (uses default) createUser('Undefined User', undefined); // User: Undefined User, Role: standard

// Note: Passing 'null' will override the default, as null is a valid value. createUser('Null User', null); // User: Null User, Role: null