JSFiddle - React, Tailwind, and code Playground

JavaScript

function sumEvenFibs() {
    var f1, f2, delta, total;

    f1 = 1;
    f2 = 2;
    total = 0;

    while (total < 4000000) {
      if (f1 % 2 === 0) {
        total += f1;
      }

      delta = f1;
      f1 = f2;
      f2 = delta + f1;
    }

    return total;
  }

  console.log(sumEvenFibs());