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map-set-weakmap.spec.js

import {strict as assert} from 'assert';

describe('Fundamentals', () => {
  it('creating a set using `new Set()` creates an empty set', () => {
    const set = new Set();
    assert.equal(set.size, 0);
  });
  it('add one item, using `add` and the size is 1', () => {
    const set = new Set();
    set.add({not: 'primitive'});
    assert.equal(set.size, 1);
  });
  it('after adding a primitive item, it`s in the Set', () => {
    const set = new Set();
    set.add(1);
    assert.equal(set.has(1), true);
  });
  it('after adding an object, we find it in the Set', () => {
    const set = new Set();
    const thisObject = {an: 'object'};
    set.add(thisObject);
    assert.equal(set.has(thisObject), true);
  });
});

describe('set.add(1) is the same as set.add("1")??', () => {
  it('adding a number 1 and a string "1" makes a Set of size 2', () => {
    const set = new Set();
    set.add(1);
    set.add('1');
    assert.equal(set.size, 2);
  });
  it('adding 1 twice creates a Set of size 1', () => {
    const set = new Set();
    set.add(1);
    set.add(1);
    assert.equal(set.size, 1);
  });
  it('adding "1" twice creates a Set of size 1', () => {
    const set = new Set();
    set.add("1");
    set.add("1");
    assert.equal(set.size, 1);
  });
  it('adding a look-alike object twice results of size 2', () => {
    const set = new Set();
    set.add(() => {});
    set.add(() => {});
    assert.equal(set.size, 2);
  });
});

describe('What happens when we add 0 and -0?', () => {
  it('adding -0 to a Set, then 0 is in the Set', () => {
    const set = new Set();
    set.add(-0);
    assert.equal(set.has(0), true);
  });

  it('-0 not equals exactly 0, using Object.is()', () => {
    assert.equal(Object.is(-0, 0), false);
  });
  it('we add -0, when iterating over the set we get 0', () => {
    // see https://tc39.es/ecma262/#sec-set.prototype.add point 4
    const set = new Set();
    set.add(-0);
    for (const value of set) {
      assert(Object.is(value, 0));
    }
  });
});

import 'expose-gc';
describe('Garbage collection for Weak* ...', () => {
  xit('a WeakMap does not hold on to its entries when gc runs', () => {
    const weakmap = new WeakMap();
    const key = new WeakRef({});
    weakmap.set(key.deref(), 42);

    // collect all your trash
    global.gc(); // requires `import 'expose-gc';`

    assert.equal(key.deref(), null);
  });
  xit('deleting the prop of an obj, which was used in the WeakMap, it wont be in the WeakMap', () => {
    const obj = {x: 1};
    const weakmap = new WeakMap();
    weakmap.set(obj.x, 42);
    delete obj.x;
    assert.equal(weakmap.has(1), false);
  });
});