Fixed small numbers parsing

.gitignore

@@ -1,4 +1,5 @@
 # Don't check auto-generated stuff into git
+.idea
 node_modules
 coverage
 lib

src/index.js

@@ -69,7 +69,15 @@ function numberToString(arg) {
     }
     return arg;
   } else if (typeof arg === 'number') {
-    return String(arg);
+    if (arg === -0) {
+      return '0';
+    }
+    // Using Intl to reliably convert number to string,
+    // toString/toFixed will give incorrect results for some numbers
+    return arg.toLocaleString('en', {
+      maximumFractionDigits: 20,
+      useGrouping: false,
+    });
   } else if (typeof arg === 'object' && arg.toString && (arg.toTwos || arg.dividedToIntegerBy)) {
     if (arg.toPrecision) {
       return String(arg.toPrecision());

src/tests/test.index.js

@@ -74,6 +74,12 @@ describe('toWei', () => {
     assert.equal(units.toWei(1, 'milli').toString(10), units.toWei(1000, 'micro').toString(10));
 
     assert.throws(() => { units.toWei(1, 'wei1'); }, Error);
+
+    assert.equal(units.toWei(0.1, 'gwei').toString(10), '100000000');
+  });
+
+  it('should return the correct value for small numbers', () => {
+    assert.equal(units.toWei(1e-7, 'gwei').toString(10), '100');
   });
 });