fix rating display for 0 point assignments

fix issue where for a 0 points assignment with a custom grading scheme,
if a rating starts with a number and contains an e, only the number
will be displayed in the gradebook and speedgrader when selected.

fixes EVAL-3672
flag=none

Test Plan:
- create a 0 point assignment with a grading scheme that has a
  custom rating with a number in front and contains the letter 'e'
  ex: '19 will do e'
- go to the gradebook and apply the rating
- confirm that the display does not only display the number but the
  whole rating
- go to speedgrader and confirm that the whole rating is displayed
- for other assignments without grading schemes, try inputting values
  in scientific format and confirm that they still work.
  ex: 2e3

Change-Id: I53411a6c3bf55b4979154127ae6ba29a785bdde5
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/334811
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Christopher Soto <christopher.soto@instructure.com>
Reviewed-by: Sleyder Zuleta <sleyder.zuleta@instructure.com>
QA-Review: Jackson Huang <jackson.huang@instructure.com>
Product-Review: Ravi Koll <ravi.koll@instructure.com>

spec/javascripts/jsx/shared/helpers/numberHelperSpec.js

@@ -17,7 +17,6 @@
  */
 
 import numberHelper from '@canvas/i18n/numberHelper'
-import I18n from '@canvas/i18n'
 import I18nStubber from 'helpers/I18nStubber'
 
 let input, output, delimiter, separator
@@ -53,7 +52,7 @@ test('uses default parse function', () => {
 
 test('returns NaN for invalid numbers', () => {
   numberHelper._parseNumber.restore()
-  ok(isNaN(numberHelper.parse('foo')))
+  ok(Number.isNaN(numberHelper.parse('foo')))
 })
 
 test('returns value of parse function', () => {
@@ -78,12 +77,12 @@ test('uses default delimiter and separator if not a valid number', () => {
 })
 
 test('returns NaN for null and undefined values', () => {
-  ok(isNaN(numberHelper.parse(null)))
-  ok(isNaN(numberHelper.parse(undefined)))
+  ok(Number.isNaN(numberHelper.parse(null)))
+  ok(Number.isNaN(numberHelper.parse(undefined)))
 })
 
 test('returns input if already a number', () => {
-  const input = 4.7
+  input = 4.7
   equal(numberHelper.parse(input), input)
 })
 
@@ -92,6 +91,21 @@ test('supports e notation', () => {
   equal(numberHelper.parse('3e2'), 300)
 })
 
+test('supports a negative exponent', () => {
+  numberHelper._parseNumber.restore()
+  equal(numberHelper.parse('3e-1'), 0.3)
+})
+
+test('supports a negative scientific notation value', () => {
+  numberHelper._parseNumber.restore()
+  equal(numberHelper.parse('-3e1'), -30)
+})
+
+test('does not support an invalid scientific notation format', () => {
+  numberHelper._parseNumber.restore()
+  ok(Number.isNaN(numberHelper.parse('19 will e')))
+})
+
 test('parses toString value of objects', () => {
   numberHelper._parseNumber.restore()
   const obj = {toString: () => `2${separator}3`}

ui/shared/i18n/numberHelper.ts

@@ -40,7 +40,7 @@ const helper = {
     }
 
     // final fallback to old parseFloat - this allows us to still support scientific 'e' notation
-    if (input.toString().match(/e/) && Number.isNaN(Number(num))) {
+    if (Number.isNaN(Number(num)) && helper.isScientific(input.toString())) {
       num = parseFloat(input)
     }
 
@@ -50,6 +50,11 @@ const helper = {
   validate(input: number | string) {
     return !Number.isNaN(Number(helper.parse(input)))
   },
+
+  isScientific(inputString: string) {
+    const scientificPattern = /^[+-]?\d+(\.\d*)?([eE][+-]?\d+)$/
+    return inputString.match(scientificPattern)
+  },
 }
 
 export default helper