fix(formatNumber): allow negative fraction size

Closes #13913

Author: jbedard

src/ng/filter/filters.js

@@ -221,18 +221,37 @@ function roundNumber(parsedNumber, fractionSize, minFrac, maxFrac) {
     var digit = digits[roundAt];
 
     if (roundAt > 0) {
-      digits.splice(roundAt);
+      // Drop fractional digits beyond `roundAt`
+      digits.splice(Math.max(parsedNumber.i, roundAt));
+
+      // Set non-fractional digits beyond `roundAt` to 0
+      for (var j = roundAt; j < digits.length; j++) {
+        digits[j] = 0;
+      }
     } else {
       // We rounded to zero so reset the parsedNumber
+      fractionLen = Math.max(0, fractionLen);
       parsedNumber.i = 1;
-      digits.length = roundAt = fractionSize + 1;
-      for (var i=0; i < roundAt; i++) digits[i] = 0;
+      digits.length = Math.max(1, roundAt = fractionSize + 1);
+      digits[0] = 0;
+      for (var i = 1; i < roundAt; i++) digits[i] = 0;
     }
 
-    if (digit >= 5) digits[roundAt - 1]++;
+    if (digit >= 5) {
+      if (roundAt - 1 < 0) {
+        for (var k = 0; k > roundAt; k--) {
+          digits.unshift(0);
+          parsedNumber.i++;
+        }
+        digits.unshift(1);
+        parsedNumber.i++;
+      } else {
+        digits[roundAt - 1]++;
+      }
+    }
 
     // Pad out with zeros to get the required fraction length
-    for (; fractionLen < fractionSize; fractionLen++) digits.push(0);
+    for (; fractionLen < Math.max(0, fractionSize); fractionLen++) digits.push(0);
 
 
     // Do any carrying, e.g. a digit was rounded up to 10

test/ng/filter/filtersSpec.js

@@ -85,6 +85,26 @@ describe('filters', function() {
       expect(num).toBe('123.100');
     });
 
+    it('should work with negative fractionSize', function() {
+      expect(formatNumber(49, pattern, ',', '.', -2)).toBe('0');
+      expect(formatNumber(50, pattern, ',', '.', -2)).toBe('100');
+      expect(formatNumber(51, pattern, ',', '.', -2)).toBe('100');
+      expect(formatNumber(1234, pattern, ',', '.', -1)).toBe('1,230');
+      expect(formatNumber(1234.567, pattern, ',', '.', -1)).toBe('1,230');
+      expect(formatNumber(1235, pattern, ',', '.', -1)).toBe('1,240');
+      expect(formatNumber(1235, pattern, ',', '.', -2)).toBe('1,200');
+      expect(formatNumber(1235, pattern, ',', '.', -3)).toBe('1,000');
+      expect(formatNumber(1235, pattern, ',', '.', -4)).toBe('0');
+      expect(formatNumber(1250, pattern, ',', '.', -2)).toBe('1,300');
+      expect(formatNumber(1000, pattern, ',', '.', -3)).toBe('1,000');
+      expect(formatNumber(1000, pattern, ',', '.', -4)).toBe('0');
+      expect(formatNumber(1000, pattern, ',', '.', -5)).toBe('0');
+      expect(formatNumber(1, pattern, ',', '.', -1)).toBe('0');
+      expect(formatNumber(1, pattern, ',', '.', -2)).toBe('0');
+      expect(formatNumber(9, pattern, ',', '.', -1)).toBe('10');
+      expect(formatNumber(501, pattern, ',', '.', -3)).toBe('1,000');
+    });
+
     it('should format numbers that round to zero as nonnegative', function() {
       expect(formatNumber(-0.01, pattern, ',', '.', 1)).toBe('0.0');
       expect(formatNumber(-1e-10, pattern, ',', '.', 1)).toBe('0.0');