2021-05-05 17:13:49 +00:00
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---
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id: 587d7b7d367417b2b2512b1c
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title: 檢查對象是否具有某個屬性
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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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我們已經學習瞭如何添加、修改和移除對象中的屬性。 但如果我們想知道一個對象中是否包含某個屬性呢? JavaScript 爲我們提供了兩種不同的方式來實現這個功能: 一個是通過 `hasOwnProperty()` 方法,另一個是使用 `in` 關鍵字。 假如我們有一個 `users` 對象,爲檢查它是否含有 `Alan` 屬性,可以這樣寫:
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```js
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users.hasOwnProperty('Alan');
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'Alan' in users;
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```
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這兩者結果都應該爲 `true`。
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# --instructions--
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2021-05-24 07:42:08 +00:00
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請完善這個函數,如果傳遞給它的對象包含四個名字 `Alan`、`Jeff`、`Sarah` 和 `Ryan`,函數返回 true,否則返回 false。
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2021-05-05 17:13:49 +00:00
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# --hints--
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2021-05-24 07:42:08 +00:00
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不應直接訪問 `users` 對象。
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```js
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assert(code.match(/users/gm).length <= 2)
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```
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`users` 對象應該只包含 `Alan`、`Jeff`、`Sarah`、`Ryan` 4 個鍵。
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2021-05-05 17:13:49 +00:00
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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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2021-05-24 07:42:08 +00:00
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如果 `Alan`、`Jeff`、`Sarah`、`Ryan` 是傳遞給函數 `isEveryoneHere` 對象的屬性,則函數應返回 `true`。
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2021-05-05 17:13:49 +00:00
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```js
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assert(isEveryoneHere(users) === true);
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```
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2021-05-24 07:42:08 +00:00
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如果傳遞給函數 `isEveryoneHere` 對象的屬性中不包含 `Alan`,則函數返回 `false`。
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2021-05-05 17:13:49 +00:00
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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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2021-05-24 07:42:08 +00:00
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如果傳遞給函數 `isEveryoneHere` 對象的屬性中不包含 `Jeff`,則函數返回 `false`。
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2021-05-05 17:13:49 +00:00
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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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2021-05-24 07:42:08 +00:00
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如果傳遞給函數 `isEveryoneHere` 對象的屬性中不包含 `Sarah`,則函數返回 `false`。
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2021-05-05 17:13:49 +00:00
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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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2021-05-24 07:42:08 +00:00
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如果傳遞給函數 `isEveryoneHere` 對象的屬性中不包含 `Ryan`,則函數返回 `false`。
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2021-05-05 17:13:49 +00:00
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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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2021-05-24 07:42:08 +00:00
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function isEveryoneHere(userObj) {
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2021-05-05 17:13:49 +00:00
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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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2021-05-24 07:42:08 +00:00
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function isEveryoneHere(userObj) {
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2021-05-05 17:13:49 +00:00
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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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2021-05-24 07:42:08 +00:00
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].every(user => userObj.hasOwnProperty(user));
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2021-05-05 17:13:49 +00:00
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}
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console.log(isEveryoneHere(users));
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```
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