JS operation select drop-down box dynamic change

1. dynamically create select

   Function createSelect (){

       Var mySelect = document. createElement_x ("select ");

       MySelect. id = "mySelect "; 

       Document. body. appendChild (mySelect );

   }

2. Add option

  Function addOption (){

       // Search for objects by id,

        Var obj = document. getElementByIdx_x ('myselect ');

        // Add an option

        Obj. add (new  Option ("text", "value "));  

  }

3. Delete All option options

  Function removeAll (){

        Var obj = document. getElementByIdx_x ('myselect ');

  

        Obj. options. length = 0; 

  }

4. delete an option

Function removeOne (){

        Var obj = document. getElementByIdx_x ('myselect ');

        // Index. The sequence number of the option to be deleted. The sequence number of the selected option is used here.

        Var index = obj. selectedIndex;

        Obj. options. remove (index ); 

  }

5. Obtain the option value.

Var obj = document. getElementByIdx_x ('myselect ');

Var index = obj. selectedIndex; // the serial number of the selected option.

Var val = obj. options [index]. value;

6. Obtain the option text

Var obj = document. getElementByIdx_x ('myselect ');

Var index = obj. selectedIndex; // the serial number of the selected option.

Var val = obj. options [index]. text;

7. Modify option

Var obj = document. getElementByIdx_x ('myselect ');

Var index = obj. selectedIndex; // the serial number of the selected option.

Var val = obj. options [index] = new Option ("new text", "new Value ");

8. Delete select

   Function removeSelect (){

         Var mySelect = document. getElementByIdx_x ("mySelect ");

        MySelect. parentNode. removeChild (mySelect );

  }