typescript-nullable/dist/index.test.js

A TypeScript Nullable<T> Type and Monad Compliant Utility Functions

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var ramda_1 = require("ramda");
var _1 = require(".");
describe('the Nullable module', function () {
    var name = 'noob noob';
    describe('isNone', function () {
        it('determines if a particular Nullable is None', function () {
            expect(_1.Nullable.isNone(null)).toBe(true);
            expect(_1.Nullable.isNone('hi')).toBe(false);
        });
        it('provides a typeguard', function () {
            var handleNullable = function (someNullable) {
                if (!_1.Nullable.isNone(someNullable)) {
                    return someNullable;
                }
                return 'value was undefined';
            };
            expect(handleNullable('oooh wee!')).toBe('oooh wee!');
            expect(handleNullable(null)).toBe('value was undefined');
        });
    });
    describe('isSome', function () {
        it('determines if a particular Nullable is a concrete value', function () {
            expect(_1.Nullable.isSome(null)).toBe(false);
            expect(_1.Nullable.isSome('hi')).toBe(true);
        });
        it('provides a typeguard', function () {
            var handleNullable = function (someNullable) {
                if (_1.Nullable.isSome(someNullable)) {
                    return someNullable;
                }
                return 'value was undefined';
            };
            expect(handleNullable('oooh wee!')).toBe('oooh wee!');
            expect(handleNullable(null)).toBe('value was undefined');
        });
    });
    describe('Nullable.map', function () {
        describe('when given a None', function () {
            it('returns a None', function () {
                var result = _1.Nullable.map(ramda_1.toUpper)(null);
                expect(result).toEqual(null);
            });
        });
        describe('when given a concrete value', function () {
            it('applies the provided function to the concrete value value', function () {
                var result = _1.Nullable.map(ramda_1.toUpper, name);
                expect(result).toEqual(ramda_1.toUpper(name));
            });
        });
    });
    describe('Nullable.andThen', function () {
        var safeDivide = ramda_1.curry(function (a, b) {
            return a === 0
                ? null
                : b / a;
        });
        describe('when we encounter a None in a composition chain', function () {
            it('gracefully handles the absence', function () {
                var result = ramda_1.compose(_1.Nullable.andThen(safeDivide(3)), _1.Nullable.andThen(safeDivide(0)), _1.Nullable.andThen(safeDivide(4)), safeDivide(2))(32);
                expect(result).toEqual(null);
            });
        });
        describe('when a composition chain works out according to plan', function () {
            it('returns our desired result', function () {
                var result = ramda_1.compose(_1.Nullable.andThen(safeDivide(3)), _1.Nullable.andThen(safeDivide(5)), _1.Nullable.andThen(safeDivide(4)), safeDivide(2))(32);
                expect(result).toEqual(32 / 2 / 4 / 5 / 3);
            });
        });
    });
    describe('Nullable.withDefault', function () {
        describe('when given a default value and a None', function () {
            it('returns the default value', function () {
                var result = _1.Nullable.withDefault(name)(null);
                expect(result).toBe(name);
            });
        });
        describe('when given a default value and a concrete value', function () {
            it('returns the concrete value value', function () {
                var result = _1.Nullable.withDefault('foo', name);
                expect(result).toBe(name);
            });
        });
    });
    describe('Nullable.ap', function () {
        describe('when the applicative Nullable is None', function () {
            it('returns a None', function () {
                var result = _1.Nullable.ap(name)(null);
                expect(result).toEqual(null);
            });
        });
        describe('when the target Nullable is None', function () {
            it('returns a None', function () {
                var result = _1.Nullable.ap(null)(ramda_1.toUpper);
                expect(result).toEqual(null);
            });
        });
        describe('when both the applicative and target Nullables are Justs', function () {
            it('applies the wrapped function in the applicative Nullable to value in the target Nullable', function () {
                var result = _1.Nullable.ap(name)(ramda_1.toUpper);
                expect(result).toEqual(ramda_1.toUpper(name));
            });
        });
        describe('lifting functions', function () {
            var addThreeNumbers = function (a) { return function (b) { return function (c) { return a + b + c; }; }; };
            describe('when everything goes according to plan', function () {
                it('lifts a "regular" function into Nullable context and returns the correct value', function () {
                    var result = ramda_1.compose(_1.Nullable.ap(3), _1.Nullable.ap(2), _1.Nullable.ap(1))(addThreeNumbers);
                    expect(result).toBe(1 + 2 + 3);
                });
            });
            describe('when we exprience an absence', function () {
                it('lifts a "regular" function into Nullable context and returns null', function () {
                    var result = ramda_1.compose(_1.Nullable.ap(3), _1.Nullable.ap(null), _1.Nullable.ap(1))(addThreeNumbers);
                    expect(result).toBe(null);
                });
            });
        });
    });
    describe('Nullable.maybe', function () {
        describe('when given a None', function () {
            it('returns the default value', function () {
                expect(_1.Nullable.maybe(7, ramda_1.add(83), null)).toBe(7);
            });
        });
        describe('when given a concrete value', function () {
            it('applies the provided function to the concrete value and returns the resulting return value', function () {
                expect(_1.Nullable.maybe(7, ramda_1.add(83), 34)).toBe(83 + 34);
            });
        });
    });
});
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