refact(formatNumber): optimisations

Author: petebacondarwin

src/ng/filter/filters.js

@@ -1,5 +1,9 @@
 'use strict';
 
+var MAX_DIGITS = 22;
+var DECIMAL_SEP = '.';
+var ZERO_CHAR = '0';
+
 /**
  * @ngdoc filter
  * @name currency
@@ -137,10 +141,16 @@ function numberFilter($locale) {
   };
 }
 
-var MAX_DIGITS = 22;
-var DECIMAL_SEP = '.';
-var ZERO_CHAR = '0';
-
+/**
+ * parse a number (as a string) into three components that can be used
+ * for formatting the number
+ * @param  {string} numStr The number to parse
+ * @return {object} An object describing this number, containing the following keys:
+ *  - d : an array of digits containing leading zeros as necessary
+ *  - i : the number of the digits in `d` that are to the left of the decimal point
+ *  - e : the exponent for numbers that would need more than `MAX_DIGITS` digits in `d`
+ *
+ */
 function parse(numStr) {
   var exponent = 0, digits, integerLen;
   var e, i, j, zeros;
@@ -184,47 +194,48 @@ function parse(numStr) {
     integerLen = 1;
   }
 
-  return { digits: digits, exponent: exponent, integerLen: integerLen };
+  return { d: digits, e: exponent, i: integerLen };
 }
 
+/**
+ * Round the parsed number to the specified number of decimal places
+ * This function changed the parsedNumber in-place
+ */
 function roundNumber(parsedNumber, fractionSize, minFrac, maxFrac) {
-    var digit = 0;
-    var digits = parsedNumber.digits;
-    var fractionLen = digits.length - parsedNumber.integerLen;
+    var digits = parsedNumber.d;
+    var fractionLen = digits.length - parsedNumber.i;
 
-    // determine fractionSize if it is not specified
-    if (isUndefined(fractionSize)) {
-      fractionSize = Math.min(Math.max(minFrac, fractionLen), maxFrac);
-    }
+    // determine fractionSize if it is not specified; `+fractionSize` converts it to a number
+    fractionSize = (isUndefined(fractionSize)) ? Math.min(Math.max(minFrac, fractionLen), maxFrac) : +fractionSize;
 
-    // Cut off unwanted digits with rounding
-    for (; fractionLen > fractionSize && digits.length; fractionLen--) {
-      digit = digits.pop();
-      // Round up if necessary
-      if (digit >= 5) digits[digits.length - 1]++;
-    }
+    // The indec of the digit to where rounding is to occur
+    var roundAt = fractionSize + parsedNumber.i;
+    var digit = digits[roundAt];
 
-    if (!digits.length) {
+    if (roundAt > 0 ) {
+      digits.splice(roundAt);
+    } else {
       // We rounded to zero so reset the parsedNumber
-      parsedNumber.integerLen = 1;
-      // If the last removed digit was >= 5 then we need to round up
-      if (digit >= 5) digits.push(1);
-      // Pad out with the necessary zeros
-      while (digits.length <= fractionSize) digits.unshift(0);
+      parsedNumber.i = 1;
+      digits.length = roundAt = fractionSize+1;
+      for(var i=0; i<roundAt; i++) digits[i] = 0;
     }
 
+    if (digit >= 5) digits[roundAt-1]++;
+
     // Pad out with zeros to get the required fraction length
-    for (; fractionLen < fractionSize; fractionLen++)  digits.push(0);
+    for (; fractionLen < fractionSize; fractionLen++) digits.push(0);
+
 
-    // Do a final clear of any carrying, e.g. the last digit was rounded up to 10
+    // Do any carrying, e.g. a digit was rounded up to 10
     var carry = digits.reduceRight(function(carry, d, i, digits) {
       d = d + carry;
       digits[i] = d % 10;
       return Math.floor(d / 10);
     }, 0);
     if (carry) {
       digits.unshift(carry);
-      parsedNumber.integerLen++;
+      parsedNumber.i++;
     }
 }
 
@@ -248,16 +259,11 @@ function roundNumber(parsedNumber, fractionSize, minFrac, maxFrac) {
  */
 function formatNumber(number, pattern, groupSep, decimalSep, fractionSize) {
 
-  if (isObject(number)) return '';
-
-  var isNegative = number < 0;
-  number = Math.abs(number);
-
-  var isInfinity = number === Infinity;
-  if (!isInfinity && !isFinite(number)) return '';
+  if (!(isString(number) || isNumber(number)) || isNaN(number)) return '';
 
+  var isInfinity = !isFinite(number);
   var isZero = false;
-  var numStr = number + '',
+  var numStr = Math.abs(number) + '',
       formattedText = '',
       parsedNumber;
 
@@ -268,8 +274,9 @@ function formatNumber(number, pattern, groupSep, decimalSep, fractionSize) {
 
     roundNumber(parsedNumber, fractionSize, pattern.minFrac, pattern.maxFrac);
 
-    var digits = parsedNumber.digits;
-    var integerLen = parsedNumber.integerLen;
+    var digits = parsedNumber.d;
+    var integerLen = parsedNumber.i;
+    var exponent = parsedNumber.e;
     var decimals = [];
     isZero = digits.reduce(function(isZero, d) { return isZero && !d; }, true);
 
@@ -305,11 +312,11 @@ function formatNumber(number, pattern, groupSep, decimalSep, fractionSize) {
       formattedText += decimalSep + decimals.join('');
     }
 
-    if (parsedNumber.exponent) {
-      formattedText += 'e+' + parsedNumber.exponent;
+    if (exponent) {
+      formattedText += 'e+' + exponent;
     }
   }
-  if (isNegative && !isZero) {
+  if (number < 0 && !isZero) {
     return pattern.negPre + formattedText + pattern.negSuf;
   } else {
     return pattern.posPre + formattedText + pattern.posSuf;