These are just my personal notes as I was working through the New to ServiceNow training modules.

In ServiceNow, I start by selecting All > Studio and then selected my app. Near the bottom of my Catalog Item app I select the Catalog Client Scripts tab and select New.

And then I create a super simple script that will create a "Hello World" alert onLoad.

And when I got to the URL for my Catalog App, "Hello World" does pop-up. Nice - it works!

Or one of these can be used:

• g_form.addInfoMessage()
• g_form.addErrorMessage()
• g_form.showFieldMessage()

function onLoad() {
  g_form.addErrorMessage("Hello World");
}