Using an IIFE seems to be the tidiest way I've found to do it. This allows you to define your constant as a function (that is immediately invoked) that returns your constant object so you can use it as normal, i.e: LABELS.appName

.constant('LABELS', (function () {
    var self = {};
    self.appName = 'MyApp';
    self.companyName = 'MyCompany';
    self.appHeader = self.appName + ' | ' + self.companyName;
    return self;
})());//function is immediately invoked here

References:

• SO answer
• Use functions (IIFE) to define AngularJS constants and values

Using an IIFE seems to be the tidiest way I've found to do it. This allows you to define your constant as a function (that is immediately invoked) that returns your constant object so you can use it as normal, i.e: LABELS.appName

.constant('LABELS', (function () {
    var self = {};
    self.appName = 'MyApp';
    self.companyName = 'MyCompany';
    self.appHeader = self.appName + ' | ' + self.companyName;
    return self;
})());//function is immediately invoked here

References:

• SO answer
• Use functions (IIFE) to define AngularJS constants and values