Issue #2350 - Part 0: Add a helper function DefaultNumberOption

This is the abstract operation that converts an option value to a number
value, checking whether it is in the allowed range, and filling in a
fallback value if necessary.

js/src/builtin/intl/CommonFunctions.js

@@ -647,6 +647,52 @@ function GetOption(options, property, type, values, fallback) {
     return fallback;
 }
 
+
+/**
+ * The abstract operation DefaultNumberOption converts value to a Number value,
+ * checks whether it is in the allowed range, and fills in a fallback value if
+ * necessary.
+ *
+ * Spec: ECMAScript Internationalization API Specification, 9.2.11.
+ */
+function DefaultNumberOption(value, minimum, maximum, fallback) {
+  assert(
+    typeof minimum === "number" && (minimum | 0) === minimum,
+    "DefaultNumberOption"
+  );
+  assert(
+    typeof maximum === "number" && (maximum | 0) === maximum,
+    "DefaultNumberOption"
+  );
+  assert(
+    fallback === undefined ||
+      (typeof fallback === "number" && (fallback | 0) === fallback),
+    "DefaultNumberOption"
+  );
+  assert(
+    fallback === undefined || (minimum <= fallback && fallback <= maximum),
+    "DefaultNumberOption"
+  );
+
+  // Step 1.
+  if (value === undefined) {
+    return fallback;
+  }
+
+  // Step 2.
+  value = ToNumber(value);
+
+  // Step 3.
+  if (Number_isNaN(value) || value < minimum || value > maximum) {
+    ThrowRangeError(JSMSG_INVALID_DIGITS_VALUE, value);
+  }
+
+  // Step 4.
+  // Apply bitwise-or to convert -0 to +0 per ES2017, 5.2 and to ensure the
+  // result is an int32 value.
+  return std_Math_floor(value) | 0;
+}
+
 /**
  * Extracts a property value from the provided options object, converts it to a
  * Number value, checks whether it is in the allowed range, and fills in a