JavaScript - Fibonacci sequence (iterative algorithm)

In this short article, we would like to show how to implement Fibonacci sequence using iterative algorithm in JavaScript.

Quick solution:

// ONLINE-RUNNER:browser;

function fibonacci(number) {
  	if(number < 1) {
    	return NaN;
    }
    var a = 0;
    var b = 1;
    for (var i = 1; i < number; ++i) {
		var c = a + b;
      	a = b;
      	b = c;
    }
    return b;
}


// Usage example:

console.log(fibonacci(1));  // 1
console.log(fibonacci(2));  // 1
console.log(fibonacci(3));  // 2
console.log(fibonacci(4));  // 3
console.log(fibonacci(5));  // 5