Initial data commit

Task/Extensible-prime-generator/JavaScript/extensible-prime-generator-1.js

@@ -0,0 +1,41 @@
+function primeGenerator(num, showPrimes) {
+  var i,
+      arr = [];
+
+  function isPrime(num) {
+    // try primes <= 16
+    if (num <= 16) return (
+      num == 2 || num == 3 || num == 5 || num == 7 || num == 11 || num == 13
+    );
+    // cull multiples of 2, 3, 5 or 7
+    if (num % 2 == 0 || num % 3 == 0 || num % 5 == 0 || num % 7 == 0)
+      return false;
+    // cull square numbers ending in 1, 3, 7 or 9
+    for (var i = 10; i * i <= num; i += 10) {
+      if (num % (i + 1) == 0) return false;
+      if (num % (i + 3) == 0) return false;
+      if (num % (i + 7) == 0) return false;
+      if (num % (i + 9) == 0) return false;
+    }
+    return true;
+  }
+
+  if (typeof num == "number") {
+    for (i = 0; arr.length < num; i++) if (isPrime(i)) arr.push(i);
+    // first x primes
+    if (showPrimes) return arr;
+    // xth prime
+    else return arr.pop();
+  }
+
+  if (Array.isArray(num)) {
+    for (i = num[0]; i <= num[1]; i++) if (isPrime(i)) arr.push(i);
+    // primes between x .. y
+    if (showPrimes) return arr;
+    // number of primes between x .. y
+    else return arr.length;
+  }
+  // throw a default error if nothing returned yet
+  // (surrogate for a quite long and detailed try-catch-block anywhere before)
+  throw("Invalid arguments for primeGenerator()");
+}