如何为“选择”框制作占位符？

“选择”标签中没有占位符属性，但它可以为“选择”框制作占位符。有很多方法可以为“选择”框创建占位符。

示例 1：

    
        
        
    
    
        
GeeksforGeeks

        

            
                Example Placeholder
                  
                
                GeeksforGeeks
                w3skul
                tuitorial point
                CodeComunity
                Coders
                
        
    
                     

输出：

示例 2：使用 JavaScript 在选择框中创建占位符。

    
        
            function populate(s, s1) {
                var s = document.getElementById(s);
                var s1 = document.getElementById(s1);
                s1.innerHTML = "";
                if(s.value == "Database") {
                    var arr = ["|Select","mysql|MySQL","oracale|Oracale"];
                }
                for(var option in arr) {
                    var pair = arr[option].split("|");
                    var new_op = document.createElement("option");
                    new_op.value = pair[0];
                    new_op.innerHTML = pair[1];
                    s1.options.add(new_op);
                }
            }
        
        
            body {
                text-align:center;
            }
            h1 {
                color:green;
            }
        
    
    
        GeeksforGeeks
        Choose Subject:
        
            Select
            Database
            Java
            Python
        
        Choose topics:
        
    
                                        

输出：