Return null coverage for Node.js and output — symbol in stats (br…

…owserslist#439)

* Simplify a temporary object with browser versions

* Node.js version should return `null` instead `0`

* Add output `—` for Node.js versions with `null` coverage

* Rename `browsersByQueryCoverage` to `browsersCoverageByQuery`

client/view/BrowserStats/browserStats.js

@@ -44,7 +44,8 @@ export function toggleShowStats(isShown) {
 }
 
 function createCoverageCell(coverage) {
-  let coveragePercentageHtmlString = cov => formatPercent(cov)
+  let coveragePercentageHtmlString = cov =>
+    cov !== null ? formatPercent(cov) : '—'
   let coveragePercentageCssString = cov => {
     let result = (Math.log(1 + cov) * 100) / Math.log(1 + 100)
     if (result === 0) {

server/lib/get-browsers.js

@@ -20,29 +20,32 @@ export default async function getBrowsers(query, region) {
       : new Error(`Unknown browser query \`${query}\`.`)
   }
 
-  let browsersNames = {}
+  let browsersCoverageByQuery = {}
+
   for (let browser of browsersByQuery) {
     let [id, version] = browser.split(' ')
-    let versionCoverage = null
+    let versionCoverage
 
-    if (id !== 'node') {
-      versionCoverage =
+    // The Node.js is not in the Can I Use db
+    if (id === 'node') {
+      versionCoverage = null
+    } else {
+      versionCoverage = roundNumber(
         region === REGION_GLOBAL
           ? getGlobalCoverage(id, version)
           : await getRegionCoverage(id, version, region)
+      )
     }
 
-    let versionData = { [`${version}`]: roundNumber(versionCoverage) }
-
-    if (!browsersNames[id]) {
-      browsersNames[id] = { versions: versionData }
-    } else {
-      Object.assign(browsersNames[id].versions, versionData)
+    if (!browsersCoverageByQuery[id]) {
+      browsersCoverageByQuery[id] = {}
     }
+
+    browsersCoverageByQuery[id][version] = versionCoverage
   }
 
-  let browsers = Object.entries(browsersNames)
-    .map(([id, { versions }]) => {
+  let browsers = Object.entries(browsersCoverageByQuery)
+    .map(([id, versions]) => {
       let name
       let coverage