JavaScript cascading drop-down list example code (self-written)_javascript skills

Html dom refers to some dom operations supported by various browsers before the emergence of the w3c specification.
1, Select object.
Attributes
a, selectedIndex: the subscript of the option selected by the user, the subscript starts from 0
b, length: Get or set the number of options
c, options: return an array, array The element is Option object
2, Options object
attributes:
a, text: the text content of the option
b, value: the value of the option
c, selected: when the option is selected , the value is true, otherwise it is false
Tips: Create an Option object

Copy code The code is as follows:

var op=new Option(text,value);

A cascading drop-down list I wrote:

The code is as follows:

Copy code The code is as follows:

Professional Choice

onchange="doAction(this.selectedIndex) ;">
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