Fix #42: Improve price string parsing.

* Update how we pull the price string from extracted Fathom price elements to provide main and subunits (e.g. dollars and cents) if available.
* Add price string cleaning methods to remove extra characters (like commas) that were causing price parsing to fail.
* Handle case when price string parsing still fails after cleaning by checking in the background script that the price string is formatted correctly before rendering the browserAction popup.
  * This will guarantee we never see the “blank panel” reported in #79 and #88.

Price element innerText strings now supported as a result of these changes:
* "$1327 /each" ([Home Depot example page](https://www.homedepot.com/p/KitchenAid-Classic-4-5-Qt-Tilt-Head-White-Stand-Mixer-K45SSWH/202546032))
* "$1,049.00" ([Amazon example page](https://www.amazon.com/Fujifilm-X-T2-Mirrorless-F2-8-4-0-Lens/dp/B01I3LNQ6M/ref=sr_1_2?ie=UTF8&qid=1535594119&sr=8-2&keywords=fuji+xt2+camera))
* "US $789.99" ([Ebay example page](https://www.ebay.com/itm/Dell-Inspiron-7570-15-6-Touch-Laptop-i7-8550U-1-8GHz-8GB-1TB-NVIDIA-940MX-W10/263827294291))
* "$4.99+" ([Etsy example page](https://www.etsy.com/listing/555504975/frankenstein-2-custom-stencil?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=&ref=sr_gallery-1-13))

Note: This does not handle the case where there is more than one price for the product page (e.g. if we see a range of prices such as "$19.92 - $38.00" or if the price changes based on size/color, etc.); that’s handled by Issue #86.

src/extraction/fathom_extraction.js

@@ -35,12 +35,76 @@ function runRuleset(doc) {
     fnodesList = fnodesList.filter(fnode => fnode.scoreFor(`${feature}ish`) >= SCORE_THRESHOLD);
     // It is possible for multiple elements to have the same highest score.
     if (fnodesList.length >= 1) {
-      extractedElements[feature] = fnodesList[0].element;
+      const element = fnodesList[0].element;
+      // Check for price units and subunits
+      if (feature === 'price' && element.children.length > 0) {
+        extractedElements[feature] = getPriceUnitElements(element);
+        continue;
+      }
+      extractedElements[feature] = element;
     }
   }
   return extractedElements;
 }
 
+/**
+ * Returns true if the string contains a number.
+ */
+function hasNumber(string) {
+  return /\d/.test(string);
+}
+
+/**
+ * Get the main and sub unit elements for the product price.
+ *
+ * @returns {Object} A string:element object with 'mainUnit' and 'subUnit' keys.
+ */
+function getPriceUnitElements(element) {
+  let isMainUnit = true;
+  const priceElements = {};
+  // Loop through children: first element containing a digit is main unit,
+  // second is subunit.
+  for (const priceSubEle of element.children) {
+    if (hasNumber(priceSubEle.innerText)) {
+      if (isMainUnit) {
+        priceElements.mainUnit = priceSubEle;
+        isMainUnit = false;
+      } else {
+        priceElements.subUnit = priceSubEle;
+      }
+    }
+  }
+  return priceElements;
+}
+
+/**
+ * Checks if a price object has subunits and returns a price string.
+ *
+ * @param {Object} If the price has subunits, an object literal, else an HTML element
+ */
+function getPriceString(priceObj) {
+  // Check for subunits e.g. dollars and cents.
+  if ('mainUnit' in priceObj) {
+    const mainUnitStr = priceObj.mainUnit.innerText;
+    const subUnitStr = priceObj.subUnit.innerText;
+    return cleanPriceString(`$${mainUnitStr}.${subUnitStr}`);
+  }
+  return cleanPriceString(priceObj.innerText);
+}
+
+
+/**
+ * Reformats price string to be of form "$NX.XX".
+ */
+function cleanPriceString(priceStr) {
+  // Remove any commas
+  let cleanedPriceStr = priceStr.replace(/,/g, '');
+  // Remove any characters preceding the '$' and following the '.XX'
+  cleanedPriceStr = cleanedPriceStr.substring(cleanedPriceStr.indexOf('$'));
+  cleanedPriceStr = cleanedPriceStr.substring(0, cleanedPriceStr.indexOf('.') + 3);
+  return cleanedPriceStr;
+}
+
 /**
  * Returns true if every key in PRODUCT_FEATURES has a truthy value.
  */
@@ -58,9 +122,14 @@ export default function extractProduct(doc) {
     for (const feature of PRODUCT_FEATURES) {
       if (feature === 'image') {
         extractedProduct[feature] = extractedElements[feature].src;
-      } else {
-        extractedProduct[feature] = extractedElements[feature].innerText;
+        continue;
+      // Clean up price string and check for subunits
+      } else if (feature === 'price') {
+        const priceStr = getPriceString(extractedElements[feature]);
+        extractedProduct[feature] = priceStr;
+        continue;
       }
+      extractedProduct[feature] = extractedElements[feature].innerText;
     }
   }
   return hasAllFeatures(extractedProduct) ? extractedProduct : null;