Maintain previous state

This code making a combo box.

public String getColor(String colorName) 
{
mySB.append("<select onchange=\"ChangeColor(this);\" style=\"font-size:0.8em;\" id=\"").append(colorName).append("\" name=\"").append(colorName).append("\">")
            .append("<option value=\"\">&nbsp;</option>");
}
function ChangeColor(colors) {
var partcolor = (colors.options[colors.selectedIndex].value);

if (partcolor=="black"){
  document.getElementById("colorRow").style.backgroundColor = 'black';
 } 
else if(partcolor=="brown")  {
 document.getElementById("colorRow").style.backgroundColor ='brown';
}   else if(partcolor=="yellow")  {
 document.getElementById("colorRow").style.backgroundColor ='yellow';
}
}

I want to d开发者_运维百科ynamically update the color selection in a combo box using JavaScript. when the page reload, previous state of colors can be maintain in a Java app.

You mention page load, so one option would be to save the color selection in a query parameter, i.e. make the browser reload the same page in ChangeColor() with a URL that includes the color choice like this: http://...myurl...?color=purple, then examine the URL parameters during onLoad().

Depending on your design, you might be able to just dynamically update the color selection using JavaScript without a page reload?

Like this:

<div id="to_update_later"></div>

<script>
    function ChangeColor(color) {
        document.getElementById("to_update_later").innerText = "The color " + color;
    }
</script>

This example shows how to replace the contents of a div tag dynamically from a JavaScript function. It is also possible to append instead of replacing. See for example http://www.w3schools.com/js/js_ex_dom.asp for tutorials on manipulating the HTML DOM objects of a web page.