JS兼容的方式来获取浏览器的宽度

<script type="text/javascript">
        
        //need to wait until onload so body is available    
        window.onload = function(){
        
            function getWindowWidth(){
                if (window.innerWidth){
                    return window.innerWidth;
                } else if (document.documentElement.clientWidth){
                    return document.documentElement.clientWidth;
                } else if (document.body.clientWidth){
                    return document.body.clientWidth;
                }
            }
            
                    
            //determine if the browser has Netscape-style plugins
            var hasNSPlugins = !!(navigator.plugins && navigator.plugins.length);
            
            //determine if the browser has basic DOM Level 1 capabilities
            var hasDOM1 = !!(document.getElementById && document.createElement && 
                           document.getElementsByTagName);
            
            alert("Window width: " + getWindowWidth());
            alert("Supports Netscape plugins? " + hasNSPlugins);
            alert("Supports Core DOM 1?
 " + hasDOM1);
        }
    </script>