git.squeep.com Git - squeep-lazy-property/blob - test/lazy.js

   1 /* eslint-env mocha */
   2 'use strict';
   3
   4 const assert = require('assert');
   5 const { lazy } = require('../index');
   6
   7 describe('lazy', function () {
   8   let o, initializer, called;
   9
  10   beforeEach(function () {
  11     o = {};
  12     called = false;
  13     initializer = () => {
  14       called = true;
  15       return 'value';
  16     };
  17   });
  18
  19   it('does not initialize if not accessed', function () {
  20     lazy(o, 'p', initializer);
  21     assert.strictEqual(called, false);
  22     assert(Object.keys(o).includes('p'));
  23   });
  24
  25   it('wants a callable initializer', function () {
  26     try {
  27       lazy(o, 'p', undefined);
  28       assert.fail('should reject un-callable initializer');
  29     } catch (e) {
  30       assert(e instanceof TypeError, `expected 'TypeError', got '${e.name}'`);
  31     }
  32   });
  33
  34   it('initializes if accessed', function () {
  35     lazy(o, 'p', initializer);
  36     const v = o.p;
  37     assert.strictEqual(called, true);
  38     assert.strictEqual(v, 'value');
  39   });
  40
  41   it('handles symbolic properties', function () {
  42     const s = Symbol('s');
  43     lazy(o, s, initializer);
  44     const v = o[s];
  45     assert.strictEqual(called, true);
  46     assert.strictEqual(v, 'value');
  47   });
  48
  49   it('can be overwritten before being read', function () {
  50     const expected = 'foobar';
  51     lazy(o, 'p', initializer);
  52     o.p = expected;
  53     const v = o.p;
  54     assert.strictEqual(v, expected);
  55     assert.strictEqual(called, false);
  56   });
  57
  58 }); // lazy