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      By referencing the HEAD element of the page first and then calling appendChild(), this means the newly created element is added to the very end of the HEAD tag. Furthermore, you should be aware that no existing element is harmed in the adding of the new element- that is to say, if you call loadjscssfile("myscript.js", "js") twice, you now end up with two new "script" elements both pointing to the same Javascript file. This is problematic only from an efficiency standpoint, as you'll be adding redundant elements to the page and using unnecessary browser memory in the process. A simple way to prevent the same file from being added more than once is to keep track of the files added by loadjscssfile(), and only load a file if it's new:

以下是引用片段：
var filesadded="" //保存已經綁定文件名字的數組變量
function checkloadjscssfile(filename, filetype){
if (filesadded.indexOf("["+filename+"]")==-1){// indexOf判斷數組里是否有某一項
  loadjscssfile(filename, filetype)
  filesadded+="["+filename+"]" //把文件名字添加到filesadded
}
else
  alert("file already added!")//如果已經存在就提示
}
checkloadjscssfile("myscript.js", "js") //success
checkloadjscssfile("myscript.js", "js") //redundant file, so file not added

      Here I'm just crudely detecting to see if a file that's set to be added already exists within a list of added files' names stored in variable filesadded before deciding whether to proceed or not.

      Ok, moving on, sometimes the situation may require that you actually remove or replace an added .js or .css file. Lets see how that's done next.

以下是引用片段：
function loadjscssfile(filename, filetype){
if (filetype=="js"){ //判斷文件類型
  var fileref=document.createElement('script')//創建標簽
  fileref.setAttribute("type","text/javascript")//定義屬性type的值為text/javascript
  fileref.setAttribute("src", filename)//文件的地址
}
else if (filetype=="css"){ //判斷文件類型
  var fileref=document.createElement("link")
  fileref.setAttribute("rel", "stylesheet")
  fileref.setAttribute("type", "text/css") 
  fileref.setAttribute("href", filename)
}
if (typeof fileref!="undefined")
  document.getElementsByTagName("head")[0].appendChild(fileref)
} 

loadjscssfile("myscript.js", "js") //打開頁面時瀏覽器動態的加載文件
loadjscssfile("javascript.php", "js") // 打開頁面時瀏覽器動態的加載"javascript.php" ，
loadjscssfile("mystyle.css", "css") //打開頁面時瀏覽器動態的加載.css 文件