Php+js+ajax+mysql realize three-level linkage between provinces and cities

The effect of the following figure:

Idea: First get the city of the selected province or the county of your choice, convert the acquired data to a Jason-formatted string return to the AJAX client, where the client uses eval to convert the string of Jason format into an object, creates a text node for each element value of the object, and creates an option node. Appends the text node to the option node and appends the option node to the Select node.

Ajax-area-select.html

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 transitional//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">  
Ajaxutil.js