fletcherist · October 11, 2017 15:13 · Oct 11, 2017
diff --git a/CpuMeter.js b/CpuMeter.js
@@ -0,0 +1,47 @@
+((name, context = window, func) => { context[name] = func() })
+  ('CpuMeter', this, () => {
+    const isEmptyObject = object => Object.keys(object).length === 0
+    const getProcessorUsage = (usage, oldUsage) =>
+      Math.floor((usage.kernel + usage.user - oldUsage.kernel - oldUsage.user) / (usage.total - oldUsage.total) * 100)
+
+    class CpuMeter {
+      constructor() {
+        if (!chrome || !chrome.system || !chrome.system.cpu) {
+          throw new Error(`No access to chrome.system.cpu!
+            Please allow permission (system.cpu) in your manifest.json`)
+        }
+        this.cpuInfo = {}
+        this.previousCpuInfo = {}
+      }
+
+      getInfo(callback) {
+        this._update().then(info => {
+          callback({
+            cpuUsage: this.getCpuUsage()
+          })
+        })
+      }
+
+      getCpuUsage() {
+        return this.cpuInfo.processors
+          .reduce((acc, processor, index) => [...acc, getProcessorUsage(
+            processor.usage,
+            this.previousCpuInfo.processors[index].usage)], [])
+          .reduce((acc, cpuUsage) => acc + cpuUsage, 0) / this.cpuInfo.processors.length
+      }
+
+      _update() {
+        return new Promise(resolve => chrome.system.cpu.getInfo(cpuInfo => {
+          this.previousCpuInfo = this.cpuInfo
+          if (isEmptyObject(this.previousCpuInfo)) {
+            this.previousCpuInfo = cpuInfo
+          }
+
+          this.cpuInfo = cpuInfo
+          resolve(cpuInfo)
+        }))
+      }
+    }
+
+    return CpuMeter
+  }, this)