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>
118 lines
2.4 KiB
Markdown
118 lines
2.4 KiB
Markdown
---
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id: 56533eb9ac21ba0edf2244c9
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title: 通过变量访问对象属性
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/cnQyKur'
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forumTopicId: 16165
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dashedName: accessing-object-properties-with-variables
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---
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# --description--
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中括号操作符的另一个使用方式是访问赋值给变量的属性。当你需要遍历对象的属性列表或访问查找表（lookup tables）时，这种方式极为有用。
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这有一个使用变量来访问属性的例子：
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```js
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var dogs = {
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Fido: "Mutt", Hunter: "Doberman", Snoopie: "Beagle"
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};
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var myDog = "Hunter";
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var myBreed = dogs[myDog];
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console.log(myBreed); // "Doberman"
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```
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使用此概念的另一种方法是在程序执行期间动态收集属性名称，如下所示：
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```js
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var someObj = {
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propName: "John"
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};
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function propPrefix(str) {
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var s = "prop";
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return s + str;
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}
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var someProp = propPrefix("Name"); // someProp now holds the value 'propName'
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console.log(someObj[someProp]); // "John"
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```
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提示：当我们通过变量名访问属性的时候，不需要给变量名包裹引号。因为实际上我们使用的是变量的值，而不是变量的名称。
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# --instructions--
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使用变量`playerNumber`，通过中括号操作符找到`testObj`中`playerNumber`为`16`的值。然后把名字赋给变量`player`。
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# --hints--
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`playerNumber`应该是一个数字。
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```js
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assert(typeof playerNumber === 'number');
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```
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变量`player`应该是一个字符串。
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```js
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assert(typeof player === 'string');
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```
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`player`点值应该是 "Montana"。
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```js
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assert(player === 'Montana');
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```
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你应该使用中括号访问`testObj`。
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```js
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assert(/testObj\s*?\[.*?\]/.test(code));
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```
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你不应该直接将`Montana`赋给`player`。
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```js
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assert(!code.match(/player\s*=\s*"|\'\s*Montana\s*"|\'\s*;/gi));
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```
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你应该在中括号中使用`playerNumber`变量。
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```js
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assert(/testObj\s*?\[\s*playerNumber\s*\]/.test(code));
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```
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# --seed--
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## --after-user-code--
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```js
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if(typeof player !== "undefined"){(function(v){return v;})(player);}
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```
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## --seed-contents--
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```js
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// Setup
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var testObj = {
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12: "Namath",
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16: "Montana",
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19: "Unitas"
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};
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// Only change code below this line
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var playerNumber; // Change this line
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var player = testObj; // Change this line
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```
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# --solutions--
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```js
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var testObj = {
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12: "Namath",
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16: "Montana",
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19: "Unitas"
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};
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var playerNumber = 16;
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var player = testObj[playerNumber];
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```
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