foo.java

// We created our link dynamically from here
@Override
	public Map<String, String> getLinks() {
		Map<String, String> links = new HashMap<String, String>();
		
		if (ModuleUtil.compareVersion(OpenmrsConstants.OPENMRS_VERSION, DIAGNOSIS_MIGRATION_LEAST_SUPPORTED_VERSION) >= 0) {
			links.put("module/emrapi/MigrateDiagnosis.form", Context.getMessageSourceService().getMessage("emrapi.migrateDiagnosis.migrateDiagnosisLink.name"));
		}
		return links;
	}

// Looking at our admin page(https://demo.openmrs.org/openmrs/admin/index.htm), the link is dynamically created by
// the above code.
// Now we wanna create an alert box when that link is clicked.

// Lets assume some JS code. We assume it compiles :)
$('#linkId').onClick(function(){
  // Just make an alert
  alert('Hey you clicked me');
});

// Buts Oooppss, we don't have the id.

Well does this make sense here?
Selecting that element using the href attribute!

$("a[href$='module/emrapi/MigrateDiagnosis.form']")...

cc: @dkayiwa