fibonacci-efficient.js

//1, 1, 2, 3, 5, 8, 13, 21

(function() {

  let result = [];

  window.fibonacci = function(n) {
    if (n < 1) {
      throw new Error("n must be greater than 0");
    }

    n -= 1;

    let start = result.length;

    if (n >= start) {
      for (var i = start; i <= n; i++) {
        if (i < 2) {
          value = 1;
        } else {
          value = result[i - 2] + result[i - 1];
        }
        result.push(value);
      }
    }

    return result[n];
  }
})();

console.log(fibonacci(100));

console.log(fibonacci(1));
console.log(fibonacci(2));
console.log(fibonacci(3));
console.log(fibonacci(4));
console.log(fibonacci(5));
console.log(fibonacci(6));
console.log(fibonacci(7));
console.log(fibonacci(8));
console.log(fibonacci(9));
console.log(fibonacci(10));

//inefficient

function fibonacci(n) {
    return n < 2 ? 1 : fibonacci(n-1) + fibonacci(n-2);
}

for(let i=0;i<10;i++) {
    console.log(fibonacci(i));
}

succinct and efficient

const fib = (function() {
    let sequence = [1,1];

    return function(n) {
        while(n >= sequence.length) {
            sequence.push(sequence[sequence.length-2] + sequence[sequence.length-1]);
        }

        return sequence[n];
    }
})();

console.log(fib(6));
console.log(fib(1000));
console.log(fib(100));
console.log(fib(10));