Uses Of JsHamcrest

Now that you’re getting familiar with JsHamcrest, you might be wondering if it can be used to do any real work. Here goes some situations where you might find JsHamcrest useful.

Unit Testing

JsHamcrest is not a testing framework, but the matcher library provided by JsHamcrest is very useful for testing since you can build really expressive test assertions.

For example, take a look at this QUnit-based test suite:

// Integrates JsHamcrest with QUnit
JsHamcrest.Integration.QUnit();

$(document).ready(function(){
    test("Array might be empty", function() {
        assertThat([], empty());
    });

    test("Array might not be empty", function() {
        assertThat([1,2,3], not(empty()));
    });
});

Besides QUnit, JsHamcrest integrates with several other JavaScript testing frameworks.

See also

JsHamcrest.Integration namespace.

Mocking Frameworks

To further improve your JavaScript testing experience, Chris Leishman created a stub/mock framework called JsMockito, which uses the matchers provided by JsHamcrest under the hood.

Object Filtering

Another great use of matchers is to easily filter lists of objects according to specific rules.

For example, let’s suppose you have a list of objects that represents a people database:

var people = [
    {name: 'Daniel',  gender: 'M', age: 20},
    {name: 'Anthony', gender: 'M', age: 52},
    {name: 'Alicia',  gender: 'F', age: 37},
    {name: 'Maria',   gender: 'F', age: 46},
    {name: 'Carl',    gender: 'M', age: 30},
    {name: 'Nicky',   gender: 'F', age: 27}
];

Let’s create some matchers to be able to filter people by gender or age:

var CustomMatchers = {
    male: function() {
        return new JsHamcrest.SimpleMatcher({
            matches: function(person) {
                return person.gender == 'M';
            }
        });
    },

    female: function() {
        return new JsHamcrest.SimpleMatcher({
            matches: function(person) {
                return person.gender == 'F';
            }
        });
    },

    middleAged: function() {
        return new JsHamcrest.SimpleMatcher({
            matches: function(person) {
                return person.age >= 40 && person.age <= 60;
            }
        });
    }
};

JsHamcrest.Integration.installMatchers(CustomMatchers);

See also

Writing Custom Matchers.

That’s all it takes! Now let’s filter some data:

// First, let's make all JsHamcrest stuff globally accessible
JsHamcrest.Integration.copyMembers(this);

filter(people, male());            // Daniel, Anthony, Carl
filter(people, female());          // Alicia, Maria, Nicky
filter(people, middleAged());      // Anthony, Maria
filter(people, not(middleAged())); // Daniel, Alicia, Carl, Nicky

filter(people, either(middleAged()).or(female())); // Anthony, Alicia, Maria, Nicky
filter(people, either(male()).or(middleAged()));   // Daniel, Anthony, Maria, Carl

filter(people, both(middleAged()).and(female()));  // Maria
filter(people, both(male()).and(middleAged()));    // Anthony

Et Cetera

We are sure JsHamcrest can do a lot more than what’s shown here. If you are doing something else with JsHamcrest, please let us know!