Null Object Pattern

Empty Collections

Imagine you work for a company that writes software for dealing with legal cases.

As you are working on a feature, you discover some code:

const legalCases: LegalCase[] = await fetchCasesFromAPI();
for (const legalCase of legalCases) {
    if(legalCase.documents != null) {
        uploadDocuments(legalCase.documents);
    }
}

Remember that we should be wary of null checks? What if some other part of the code forgot to check for a null array?

The Null Object pattern can help: you create an object that represents an empty or null object.

Fixing It Up

Let's look at the fetchCasesFromAPI() method. We'll apply a version of this pattern that's a very common practice in JavaScript and TypeScript when dealing with arrays:

const fetchCasesFromAPI = async function() {
    const legalCases: LegalCase[] = await $http.get('legal-cases/');
    for (const legalCase of legalCases) {
        // Null Object Pattern...