2018-10-10 22:03:03 +00:00
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---
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id: 587d7b7d367417b2b2512b1c
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2021-03-15 03:20:39 +00:00
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title: 检查对象是否具有某个属性
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2018-10-10 22:03:03 +00:00
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challengeType: 1
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2020-08-04 07:14:21 +00:00
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forumTopicId: 301155
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2021-01-13 02:31:00 +00:00
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dashedName: check-if-an-object-has-a-property
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2021-03-15 03:20:39 +00:00
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我们已经学习了如何添加、修改和移除对象中的属性。 但如果我们想知道一个对象中是否包含某个属性呢? JavaScript 为我们提供了两种不同的方式来实现这个功能: 一个是通过 `hasOwnProperty()` 方法,另一个是使用 `in` 关键字。 假如我们有一个 `users` 对象,为检查它是否含有 `Alan` 属性,可以这样写:
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2020-08-04 07:14:21 +00:00
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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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2021-03-15 03:20:39 +00:00
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这两者结果都应该为 `true`。
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2021-03-15 03:20:39 +00:00
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我们已经定义了一个包含若干用户信息的 `users` 对象和一个 `isEveryoneHere` 函数,该函数接收 `users` 对象作为参数。 请完成该函数使其在 `users` 对象中同时包含 `Alan`、`Jeff`、`Sarah`、`Ryan` 四个属性时才返回 `true`,否则返回 `false`。
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2020-12-16 07:37:30 +00:00
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# --hints--
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2021-03-15 03:20:39 +00:00
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`users` 对象应该只包含 `Alan`、`Jeff`、`Sarah`、`Ryan` 4 个属性。
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2020-12-16 07:37:30 +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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2018-10-10 22:03:03 +00:00
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```
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2021-03-15 03:20:39 +00:00
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`isEveryoneHere` 函数在 `users` 对象包含 `Alan`、`Jeff`、`Sarah`、`Ryan` 4 个属性时应返回 `true`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(isEveryoneHere(users) === true);
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```
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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`isEveryoneHere` 函数在 `users` 对象不包含 `Alan` 时应返回 `false`。
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2018-10-10 22:03:03 +00:00
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```js
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2020-12-16 07:37:30 +00:00
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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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2018-10-10 22:03:03 +00:00
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```
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2021-03-15 03:20:39 +00:00
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`isEveryoneHere` 函数在 `users` 对象不包含 `Jeff` 时应返回 `false`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +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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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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`isEveryoneHere` 函数在 `users` 对象不包含 `Sarah` 时应返回 `false`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +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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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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`isEveryoneHere` 函数在 `users` 对象不包含 `Ryan` 时应返回 `false`。
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2018-10-10 22:03:03 +00:00
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```js
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2020-12-16 07:37:30 +00:00
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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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2018-10-10 22:03:03 +00:00
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```
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2020-08-04 07:14:21 +00:00
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2021-01-13 02:31:00 +00:00
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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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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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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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