如何在JavaScript中設置輸入選擇（HTML）中的字段？

Question

我將隨機選擇一個數字，並使用排序後的數字定義選擇的字段。我如何設置領域？

Answer 1

將選定屬性selected =「selected」添加到要選擇的選項元素。

僞代碼

function foo() 
{ 
create list of option elements 
generate random number 
get a single option element at index of random number 
set all options attribute "selected" = null 
set the option element[at index of random number] attribute selected = "selected" 
} 

Answer 2

var randomNumber = 3; // just for example 
document.getElementById('select_field').selectedIndex = randomNumber;