153 lines
3.0 KiB
Markdown
153 lines
3.0 KiB
Markdown
---
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id: 587d7b7d367417b2b2512b1c
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title: Check if an Object has a Property
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challengeType: 1
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forumTopicId: 301155
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dashedName: check-if-an-object-has-a-property
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---
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# --description--
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Now we can add, modify, and remove keys from objects. But what if we just wanted to know if an object has a specific property? JavaScript provides us with two different ways to do this. One uses the `hasOwnProperty()` method and the other uses the `in` keyword. If we have an object `users` with a property of `Alan`, we could check for its presence in either of the following ways:
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```js
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users.hasOwnProperty('Alan');
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'Alan' in users;
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// both return true
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```
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# --instructions--
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We've created an object, `users`, with some users in it and a function `isEveryoneHere`, which we pass the `users` object to as an argument. Finish writing this function so that it returns `true` only if the `users` object contains all four names, `Alan`, `Jeff`, `Sarah`, and `Ryan`, as keys, and `false` otherwise.
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# --hints--
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The `users` object should only contain the keys `Alan`, `Jeff`, `Sarah`, and `Ryan`
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```js
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assert(
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'Alan' in users &&
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'Jeff' in users &&
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'Sarah' in users &&
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'Ryan' in users &&
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Object.keys(users).length === 4
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);
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```
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The function `isEveryoneHere` should return `true` if `Alan`, `Jeff`, `Sarah`, and `Ryan` are properties on the `users` object
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```js
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assert(isEveryoneHere(users) === true);
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```
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The function `isEveryoneHere` should return `false` if `Alan` is not a property on the `users` object
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```js
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assert(
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(function () {
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delete users.Alan;
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return isEveryoneHere(users);
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})() === false
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);
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```
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The function `isEveryoneHere` should return `false` if `Jeff` is not a property on the `users` object
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```js
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assert(
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(function () {
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delete users.Jeff;
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return isEveryoneHere(users);
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})() === false
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);
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```
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The function `isEveryoneHere` should return `false` if `Sarah` is not a property on the `users` object
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```js
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assert(
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(function () {
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delete users.Sarah;
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return isEveryoneHere(users);
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})() === false
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);
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```
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The function `isEveryoneHere` should return `false` if `Ryan` is not a property on the `users` object
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```js
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assert(
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(function () {
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delete users.Ryan;
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return isEveryoneHere(users);
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})() === false
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);
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```
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# --seed--
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## --seed-contents--
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```js
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let users = {
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Alan: {
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age: 27,
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online: true
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},
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Jeff: {
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age: 32,
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online: true
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},
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Sarah: {
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age: 48,
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online: true
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},
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Ryan: {
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age: 19,
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online: true
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}
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};
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function isEveryoneHere(obj) {
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// Only change code below this line
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// Only change code above this line
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}
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console.log(isEveryoneHere(users));
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```
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# --solutions--
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```js
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let users = {
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Alan: {
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age: 27,
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online: true
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},
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Jeff: {
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age: 32,
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online: true
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},
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Sarah: {
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age: 48,
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online: true
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},
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Ryan: {
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age: 19,
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online: true
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}
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};
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function isEveryoneHere(obj) {
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return [
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'Alan',
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'Jeff',
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'Sarah',
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'Ryan'
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].every(i => obj.hasOwnProperty(i));
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}
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console.log(isEveryoneHere(users));
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```
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