Javascript intermediate link drop-down list

Htmldom refers to some dom operations supported by various browsers before w3c standards emerge. 1. Select object. Attribute a, selectedIndex: subscript of the selected option, subscript starting from 0 B, length: Get or set the number of options c, options: returns an array,... SyntaxHighlighter.

Html dom refers to some dom operations supported by various browsers before w3c standards emerge.
1. Select object.

Attribute

A, selectedIndex: subscript of the selected option. The subscript starts from 0.

B, length: Get or set the number of options
C, options: returns an array. The array element is an Option object.
2. Options object

Attribute:

A, text: Option text content

B, value: option ??

C, selected: If this option is selected, the value is true; otherwise, the value is false.

TIPS: Create an Option object

[Html]
Var op = new Option (text, value );

Var op = new Option (text, value );

A cascade drop-down list I wrote:

 
 

The Code is as follows:

[Html]