Inputs to Functions
Parameters are the named variables in the function definition.
Arguments are the actual values passed when you call the function.
JavaScript Tutorial
JavaScript Parameters and Arguments
Parameters are the placeholders in a function definition, and arguments are the values you pass in.
Understanding the difference makes function calls clearer and safer.
Why We Need It
Most bugs in functions come from unexpected inputs or missing values.
Clear parameter handling keeps your functions predictable.
Syntax
function name(param1, param2) { ... }
name(arg1, arg2)Basic Example
1. Basic usage
function greet(name) {
return "Hello " + name;
}
console.log(greet("Neha"));name is a parameter, and 'Neha' is the argument.
Real World Example
2. Missing argument
function label(status) {
return status ?? "pending";
}
console.log(label());Missing arguments become undefined.
Multiple Use Cases
Default and Optional Values
If an argument is missing, its parameter becomes undefined.
Use default parameters to handle missing values safely.
Argument Flexibility
JavaScript does not enforce parameter count. Extra arguments are ignored unless you capture them.
Use rest parameters to collect extra values.
More Examples
3. Extra arguments
function add(a, b) {
return a + b;
}
console.log(add(2, 3, 4));Extra arguments are ignored unless you collect them.
4. Rest parameters
function sum(...nums) {
return nums.reduce((acc, n) => acc + n, 0);
}
console.log(sum(1, 2, 3));Rest parameters collect extra arguments into an array.
Comparison
Without
function greet(name) {
return "Hello " + name;
}
console.log(greet());With
function greet(name = "Guest") {
return "Hello " + name;
}
console.log(greet());Common Mistakes and Fixes
Assuming required arguments
Validate inputs or provide defaults.
Using arguments object in arrows
Arrow functions do not have their own arguments object.
Mixing parameter order
Keep parameter order stable and well-documented.
Interview Questions
What is a parameter?
A named input in a function definition.
What is an argument?
The actual value passed to a function call.
How do you handle extra arguments?
Use rest parameters to capture them.
Practice Problem
Practice: Write a function that takes two parameters and returns their difference.
// TODO: function diff(a, b)
One Possible Solution
function diff(a, b) {
return a - b;
}
console.log(diff(10, 4));Frequently Asked Questions
What is the difference between parameters and arguments?
Parameters are named inputs; arguments are the values passed.
What happens if I pass fewer arguments?
Missing parameters become undefined.
Can I pass more arguments?
Yes, extra arguments are ignored unless you capture them.
Try It Yourself
Try passing different arguments and see how outputs change.