Comply with ESM syntax.

Project-Euler/Problem001.js

@@ -0,0 +1,18 @@
+// https://projecteuler.net/problem=1
+/*    Multiples of 3 and 5
+    If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
+Find the sum of all the multiples of 3 or 5 below the provided parameter value number.
+*/
+
+const multiplesThreeAndFive = (num) => {
+  let total = 0
+  // total for calculating the sum
+  for (let i = 0; i < num; i++) {
+    if (i % 3 === 0 || i % 5 === 0) {
+      total += i
+    }
+  }
+  return total
+}
+
+export { multiplesThreeAndFive }