ee1e8abd87
* feat(tools): add seed/solution restore script * chore(curriculum): remove empty sections' markers * chore(curriculum): add seed + solution to Chinese * chore: remove old formatter * fix: update getChallenges parse translated challenges separately, without reference to the source * chore(curriculum): add dashedName to English * chore(curriculum): add dashedName to Chinese * refactor: remove unused challenge property 'name' * fix: relax dashedName requirement * fix: stray tag Remove stray `pre` tag from challenge file. Signed-off-by: nhcarrigan <nhcarrigan@gmail.com> Co-authored-by: nhcarrigan <nhcarrigan@gmail.com>
86 lines
2.5 KiB
Markdown
86 lines
2.5 KiB
Markdown
---
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id: 9d7123c8c441eeafaeb5bdef
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title: 使用 slice 而不是 splice 从数组中移除元素
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challengeType: 1
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forumTopicId: 301236
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dashedName: remove-elements-from-an-array-using-slice-instead-of-splice
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---
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# --description--
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使用数组时经常遇到要删除一些元素并保留数组剩余部分的情况。为此，JavaScript 提供了`splice`方法，它接收两个参数：从哪里开始删除项目的索引，和要删除的项目数。如果没有提供第二个参数，默认情况下是移除到结尾的元素。但`splice`方法会改变调用它的原始数组。举个例子：
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```js
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var cities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
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cities.splice(3, 1); // Returns "London" and deletes it from the cities array
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// cities is now ["Chicago", "Delhi", "Islamabad", "Berlin"]
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```
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正如我们在上一次挑战中看到的那样，`slice`方法不会改变原始数组，而是返回一个可以保存到变量中的新数组。回想一下，`slice`方法接收两个参数，从开始索引开始选取到结束（不包括该元素），并在新数组中返回这些元素。使用`slice`方法替代`splice`有助于避免数组变化产生的副作用。
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# --instructions--
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用`slice`代替`splice`重写`nonMutatingSplice`函数。将`cities`数组长度限制为3，并返回一个仅包含前 3 项的新数组。
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不要改变提供给函数的原始数组。
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# --hints--
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应该使用`slice`方法。
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```js
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assert(code.match(/\.slice/g));
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```
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不能使用`splice`方法。
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```js
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assert(!code.match(/\.splice/g));
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```
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不能改变`inputCities`数组。
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```js
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assert(
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JSON.stringify(inputCities) ===
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JSON.stringify(['Chicago', 'Delhi', 'Islamabad', 'London', 'Berlin'])
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);
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```
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`nonMutatingSplice(['Chicago', 'Delhi', 'Islamabad', 'London', 'Berlin'])`应返回`['Chicago', 'Delhi', 'Islamabad']`。
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```js
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assert(
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JSON.stringify(
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nonMutatingSplice(['Chicago', 'Delhi', 'Islamabad', 'London', 'Berlin'])
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) === JSON.stringify(['Chicago', 'Delhi', 'Islamabad'])
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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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function nonMutatingSplice(cities) {
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// Only change code below this line
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return cities.splice(3);
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// Only change code above this line
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}
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var inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
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nonMutatingSplice(inputCities);
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```
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# --solutions--
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```js
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function nonMutatingSplice(cities) {
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// Only change code below this line
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return cities.slice(0,3);
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// Only change code above this line
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}
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var inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
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nonMutatingSplice(inputCities);
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```
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