Recursion is a powerful concept in programming that involves a function calling itself. It can be a bit tricky to grasp at first, but once you understand the fundamentals, it becomes a valuable tool in solving complex problems. We'll explore recursion in JavaScript with easy-to-understand examples.
Recursion occurs when a function calls itself, either directly or indirectly. It's similar to a loop, but it may involve breaking a problem down into smaller, more manageable sub-problems.
Let's start with a simple example: a countdown function.
function countdown(num) {
// Base case
if (num <= 0) {
console.log('Blastoff!');
return;
}
// Recursive case
console.log(num);
countdown(num - 1);
}
// Call the function
countdown(5);
In this example:
num
becomes less than or equal to 0, the function prints "Blastoff!" and stops calling itself.num
and calls itself with num - 1
.Now, let's look at a classic example of recursion: calculating the factorial of a number.
function factorial(n) {
// Base case
if (n === 0 || n === 1) {
return 1;
}
// Recursive case
return n * factorial(n - 1);
}
// Test the function
console.log(factorial(5)); // Output: 120
In this example:
n
is 0 or 1, the function returns 1.n
by the factorial of n - 1
.Every recursive function should have at least one base case, a condition where the function stops calling itself. Without a base case, the recursion would continue indefinitely, leading to a stack overflow.
The recursive case defines how the function calls itself with a smaller or simpler version of the problem.
Pros:
Cons:
Recursion is a valuable technique that simplifies complex problems by breaking them into smaller, more manageable sub-problems. Understanding base cases and recursive cases is crucial for implementing effective recursive solutions in JavaScript.
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