One of the many implementations of Fibonacci number in JavaScript. For other ways, visit stackoverflow.

First code is the initial step to reconstruct the formula, second code is using loop within function and last one is using recursion to list Fibonacci number.

Edit in JSFiddle, open console from DevTools and hit the Result/JavaScript.

var a = 0, // 1st nu.
    b = 1, // 2nd nu.
    res = [0, 1];
//  1st nu. + 2nd nu.
a = a + b; // 0 + 1;
res.push(a); // 1

a = a + b; // 1 + 1
res.push(a); // 2

a = a + b; // 2 + 1
res.push(a); // 3

// 2nd nu. = 1st nu. - 2nd nu.
// 1st nu. = 1st nu. + 2nd nu.
b = a - b; // 3 - 1
a = a + b; // 3 + 2; 
res.push(a); // 5

b = a - b; // 5 - 2
a = a + b; // 5 + 3; 
res.push(a); // 8

b = a - b;
a = a + b; //   8 + 5; 
res.push(a); // 13

b = a - b;
a = a + b; //   13 + 8; 
res.push(a); // 21

b = a - b;
a = a + b; //   21 + 13; 
res.push(a); // 34

console.log(res);
#=> prints [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]


var fibonacci = console.log((function(n) {
  var a = 0,
    b = 1,
    res = [a, b];

  for (var i = 0; i < n; i++) {
    if (i > 2) { // for numbers larger than 2
      b = a - b; // 2nd nu. =  1st nu. - 2nd nu.  
    }
    a = a + b; // all numbers calclulated usign 1st nu. = 1st nu. + 2nd nu.
    res.push(a);
  }
  return res;
})(11));
#=> prints [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144]

function fibonacciRecursion(n) {
  console.log(calcFibonacci(n));
}

function calcFibonacci(n) {
  var a = 0,
    b = 1,
    res = [a, b];

  for (var i = 0; i < n; i++) {
    if (i > 2) {
      b = a - b;
    }
    a = a + b;
    res.push(a);
  }

  return res;
}

fibonacciRecursion(11);
#=> prints [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144]