add getUnits()

README.md

@@ -99,6 +99,14 @@ Qty.parse('foo') // => null
 Qty.getKinds(); // => Array of names of every well-known kind of units
 ```
 
+### Available units of a particular kind
+
+```javascript
+Qty.getUnits('currency'); // => [ 'dollar', 'cents' ]
+// Or all alphabetically sorted
+Qty.getUnits(); // => [ 'acre','Ah','ampere','AMU','angstrom']
+```
+
 ### Quantity compatibility, kind and various queries
 
 ```javascript

spec/quantitiesSpec.js

@@ -1239,6 +1239,18 @@ describe("js-quantities", function() {
     });
   });
 
+  describe("Qty.getUnits", function() {
+    it("should return an array of units of kind", function() {
+      expect(Qty.getUnits("currency")).toContain("dollar");
+    });
+    it("should return an array of all units without arg", function () {
+      expect(Qty.getUnits()).toContain("sievert");
+    });
+    it("should throw unknown kind", function () {
+      expect(function () {Qty.getUnits('bogusKind')}).toThrow("Kind not recognized");
+    });
+  });
+
   describe("information", function() {
     describe("bits and bytes", function() {
       it("should have 'information' as kind", function() {

src/quantities.js

@@ -488,6 +488,41 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
     }));
   };
 
+  /**
+   * Returns a list of available units of kind
+   *
+   * @param {string} [kind]
+   * @returns {array} names of units
+   * @throws {QtyError} if kind is unknown
+   */
+  Qty.getUnits = function(kind) {
+    var units = [];
+    var unitKeys = Object.keys(UNITS);
+    if (typeof kind === 'undefined') {
+      for(var i = 0; i < unitKeys.length; i++) {
+        if (['', 'prefix'].indexOf(UNITS[unitKeys[i]][2]) == -1) {
+          units.push(unitKeys[i].substr(1, unitKeys[i].length - 2));
+        }
+      }
+    }
+    else if (Qty.getKinds().indexOf(kind) === -1) {
+      throw new QtyError('Kind not recognized');
+    }
+    else {
+      for(var i = 0; i < unitKeys.length; i++) {
+        if (UNITS[unitKeys[i]][2] === kind) {
+          units.push(unitKeys[i].substr(1, unitKeys[i].length - 2));
+        }
+      }
+    }
+
+    return units.sort(function(a, b){
+      if(a.toLowerCase() < b.toLowerCase()) return -1;
+      if(a.toLowerCase() > b.toLowerCase()) return 1;
+      return 0;
+    });
+  };
+
   /**
    * Default formatter
    *
@@ -1791,6 +1826,7 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
       OUTPUT_MAP[unitDef] = definition[0][0];
     }
   }
+
   var PREFIX_REGEX = Object.keys(PREFIX_MAP).sort(function(a, b) {
     return b.length - a.length;
   }).join("|");