Javascript dynamically sets the code _ form special effect of the value of the option of a known select statement

When you know the value of a selectoptions, determine whether the options Value of the current select statement is the same as the known value. Generally, users modify pages. The Code is as follows:

Funtion setSelectOption (a, B) {// a => select id, B => value of the known option

For (I = 0; I <$ (). length; I ++) // $ (a) to obtain the id of a, provided that prototype must be referenced. js
If ($ (a). options [I]. value = B) {// traverse select
$ (A). options [I]. selected = true; // select a specific value
Break;
}