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<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <title>Javascript clientWidth and clientHeight property</title> </head> <body> <script> function windowSize(){ var w = document.documentElement.clientWidth; var h = document.documentElement.clientHeight; alert("Width: " + w + ", " + "Height: " + h); } </script> <button type="button" onclick="windowSize();">Get Window Size</button> </body> </html>