diff --git a/FocusBlur-tab-detection.md b/FocusBlur-tab-detection.md
new file mode 100644
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--- /dev/null
+++ b/FocusBlur-tab-detection.md
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+Detect tab change in react, class base:
+
+```
+componentDidMount() {
+    window.addEventListener("focus", this.onFocus)
+}
+
+componentWillUnmount() {
+    window.removeEventListener("focus", this.onFocus)
+}
+
+onFocus = () => {
+    //
+}
+```
\ No newline at end of file