Question

I have this javscript that I wrote, and I want the “else” event to happen when bgimage does not equal 7. I have looked into this issue and am unclear about how to check if the variable is null or not defined. Currently, when bgimage does not equal 7, the Firebug just says “bgimage is not defined.”

Thanks for teaching me how to do this in advance.

if (bgimage == 7)
{
document.writeln("\n<img src='/v/vspfiles/templates/donnell/images/Company/services_bg.jpg' id='bg' />");
}
else
{
showImage();
} 

Answer 1

If bgimage has not been declared with var in the current or higher scope (or assigned a value as a global variable without var) when you use it in an if statement you will get that error. You can test for that as follows:

if (typeof bgimage === "undefined") {
    // hasn't been declared, or is set to undefined
    // do something
} else if (bgimage == 7) {
    // etc

Or test in one line:

if (typeof bgimage != "undefined" && bgimage == 7) {