85 lines
2.0 KiB
Markdown
85 lines
2.0 KiB
Markdown
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---
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id: 587d7daf367417b2b2512b7e
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title: Understand the Constructor Property
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challengeType: 1
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forumTopicId: 301327
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dashedName: understand-the-constructor-property
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---
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# --description--
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There is a special `constructor` property located on the object instances `duck` and `beagle` that were created in the previous challenges:
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```js
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let duck = new Bird();
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let beagle = new Dog();
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console.log(duck.constructor === Bird); //prints true
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console.log(beagle.constructor === Dog); //prints true
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```
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Note that the `constructor` property is a reference to the constructor function that created the instance. The advantage of the `constructor` property is that it's possible to check for this property to find out what kind of object it is. Here's an example of how this could be used:
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```js
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function joinBirdFraternity(candidate) {
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if (candidate.constructor === Bird) {
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return true;
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} else {
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return false;
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}
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}
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```
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**Note**
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Since the `constructor` property can be overwritten (which will be covered in the next two challenges) it’s generally better to use the `instanceof` method to check the type of an object.
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# --instructions--
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Write a `joinDogFraternity` function that takes a `candidate` parameter and, using the `constructor` property, return `true` if the candidate is a `Dog`, otherwise return `false`.
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# --hints--
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`joinDogFraternity` should be defined as a function.
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```js
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assert(typeof joinDogFraternity === 'function');
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```
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`joinDogFraternity` should return true if`candidate` is an instance of `Dog`.
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```js
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assert(joinDogFraternity(new Dog('')) === true);
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```
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`joinDogFraternity` should use the `constructor` property.
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```js
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assert(/\.constructor/.test(code) && !/instanceof/.test(code));
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```
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# --seed--
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## --seed-contents--
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```js
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function Dog(name) {
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this.name = name;
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}
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// Only change code below this line
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function joinDogFraternity(candidate) {
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}
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```
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# --solutions--
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```js
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function Dog(name) {
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this.name = name;
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}
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function joinDogFraternity(candidate) {
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return candidate.constructor === Dog;
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}
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```
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