JavaScript: Which String Are We Talking About Here?

Recently I helped someone troubleshoot a script problem that turned out to be a case of mistaken identity: the script's author thought she had a Java String instance, but in fact she had a JavaScript String instance — and that led to some badly broken code.

If "Huh?" or "Less gobbledegook, please!" is your reaction, you might want to read on...

The broken script looked like this:

var gr = new GlideRecord('cmdb_ci_computer');
gr.addQuery('name', 'ovrhf003');
gr.query();
gr.next();
var domain = gr.getValue('os_domain');
gs.log(domain.contains('ROCOCO'));

When run, this script generates a big, fat old "undefined". What gives?

The problem is that the string value returned by the gr.getValue('os_domain') invocation is a JavaScript String instance — and the JavaScript String class does not contain a .contains() method. That's a method from the Java String class. We troubleshot it with this logging code:

var gr = new GlideRecord('cmdb_ci_computer');
gr.addQuery('name', 'ovrhf003');
gr.query();
gr.next();
var domain = new Packages.java.lang.String(gr.getValue('os_domain'));
gs.log(typeof domain);

When we ran this, the log showed "string" — meaning that it was a JavaScript String instance. Fortunately, it's very easy to convert the JavaScript String to a Java String:

var gr = new GlideRecord('cmdb_ci_computer');
gr.addQuery('name', 'ovrhf003');
gr.query();
gr.next();
var domain = new Packages.java.lang.String(gr.getValue('os_domain'));
gs.log(domain.contains('ROCOCO'));

This code works fine. While this example is kind of silly (see below for a better alternative), it's a good example of something to keep in mind when you get results in a script that you can't otherwise explain. Maybe you've got a JavaScript class instance where you expected a Java class instance, or vice versa.

Here's an even better way to handle the problem above: this approach has the advantage of (a) working, and (b) avoiding conversion to a Java class instance:

var gr = new GlideRecord('cmdb_ci_computer');
gr.addQuery('name', 'ovrhf003');
gr.query();
gr.next();
var domain = gr.getValue('os_domain');
gs.log(domain.indexOf('ROCOCO') >= 0);

Today's photo is a close-up of the strings in a cactus stem. Pretty stringy, eh?