Fix errors and add tests

index.js

 // Default Excel value
 const decimalPlaces = 2;
+const locale = 'ru-RU';
 
 export default function format(v, type='', str=''){
     if(type === '' && str === ''){
@@ -7,7 +8,7 @@ export default function format(v, type='', str=''){
     }
 
     // TODO: document possible type values somewhere(if not already)?
-    switch(v.toLowerCase()){
+    switch(type.toLowerCase()){
     case 'number':
         return numberFormat(v);
     case 'currency':
@@ -48,7 +49,7 @@ export function basicFormat(x){
         return x.toExponential();
     }
 
-    return x.toString();
+    return x.toLocaleString(); // for proper decimal separator
 };
 
 /**
@@ -62,10 +63,11 @@ export function numberFormat(x){
         throw new Error('Unable to format non-numeric and invalid values!');
     } else {
         return parseFloat(x).toLocaleString(
-            undefined, // use OS locale
+            locale,
             {
                 minimumFractionDigits: decimalPlaces,
-                maximumFractionDigits: decimalPlaces
+                maximumFractionDigits: decimalPlaces,
+                useGrouping: false
             }
         );
     }
@@ -82,7 +84,7 @@ export function currencyFormat(x){
         throw new Error('Unable to format non-numeric and invalid values!');
     } else {
         return parseFloat(x).toLocaleString(
-            undefined, {
+            locale, {
                 style: 'currency', currency: 'RUR' 
             }
         );

package.json

@@ -16,7 +16,7 @@
     "d3": "^4.2.0"
   },
   "devDependencies": {
-    "babel-preset-es2015": "^6.9.0",
+    "babel-preset-es2015": "^6.13.2",
     "babel-register": "^6.11.6",
     "expect.js": "^0.3.1",
     "mocha": "^3.0.0"

test/test_format.js

@@ -10,4 +10,25 @@ describe('format', ()=>{
         expect(format(1e-10)).to.be('1e-10');
         expect(format(1e10)).to.be('1e+10');
     });
+
+    it('should do number formatting', function(){
+        expect(format(0, 'number')).to.be('0,00');
+        expect(format(1, 'number')).to.be('1,00');
+        expect(format(-1, 'number')).to.be('-1,00');
+        expect(format(1e10, 'number')).to.be('10000000000,00');
+        expect(format(1.1234, 'number')).to.be('1,12');
+        expect(format(1.1289, 'number')).to.be('1,13');
+        expect(() => format('123not-a-number', 'number')).to.throwError();
+    });
+
+    it('should do currency formatting', function(){
+        // Spaces should be non-breaking(ASCII 160/0xA0)
+        expect(format(0, 'currency')).to.be('0,00\xa0р.');
+        expect(format(1, 'currency')).to.be('1,00\xa0р.');
+        expect(format(-1, 'currency')).to.be('-1,00\xa0р.');
+        expect(format(1e10, 'currency')).to.be('10\xa0000\xa0000\xa0000,00\xa0р.');
+        expect(format(1.1234, 'currency')).to.be('1,12\xa0р.');
+        expect(format(1.1289, 'currency')).to.be('1,13\xa0р.');
+        expect(() => format('123not-a-number', 'currency')).to.throwError();
+    });
 });