Default Parameters

The arguments object only contains explicitly passed arguments, not default values. When a function is called and a parameter uses its default value (either because the corresponding argument was not provided or because `undefined` was explicitly passed), that default value doesn't appear in the `arguments` object. For example, in `function test(a = 1) { console.log(arguments[0], a); }`, calling `test()` would log `undefined, 1`—the `arguments` object doesn't have a value at index 0, but the parameter `a` receives its default value of 1. Similarly, `arguments.length` reflects only the number of arguments that were explicitly passed, not the number of parameters that received values (including defaults). This separation allows default parameters to coexist with code that uses the `arguments` object, though modern JavaScript often favors rest parameters (`...args`) over the `arguments` object for better clarity and compatibility with arrow functions.