function safeHtml(a){//轉譯html程式碼
    var s="";
    for(var i=0;i<a.length;i++){
        var arg=String(a);
        s=arg.replace(/&/g,"&amp;").replace(/</g,"&lt;").replace(/>/g,"&gt;");
        console.log(s);
    }
    return s;
}

window.onload=function(){

    var txt=document.getElementById
 
("txt");
    var btn=document.getElementById("btn");
    btn.onclick=function(){
        var ss=txt.value;

        var xx=safeHtml(ss);
        var div = document.getElementById('div');
        div.innerHTML=xx;

    }

}