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>
129 lines
2.7 KiB
Markdown
129 lines
2.7 KiB
Markdown
---
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id: 56533eb9ac21ba0edf2244be
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title: 全局作用域和函数
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/cQM7mCN'
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forumTopicId: 18193
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dashedName: global-scope-and-functions
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---
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# --description--
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在 JavaScript 中，<dfn>作用域</dfn>涉及到变量的作用范围。在函数外定义的变量具有 <dfn>全局</dfn> 作用域。这意味着，具有全局作用域的变量可以在代码的任何地方被调用。
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这些没有使用`var`关键字定义的变量，会被自动创建在全局作用域中，形成全局变量。当在代码其他地方无意间定义了一个变量，刚好变量名与全局变量相同，这时会产生意想不到的后果。因此你应该总是使用var关键字来声明你的变量。
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# --instructions--
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在函数外声明一个`全局`变量`myGlobal`，并给它一个初始值`10`
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在函数`fun1`的内部，**不**使用`var`关键字来声明`oopsGlobal`，并赋值为`5`。
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# --hints--
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应定义`myGlobal`。
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```js
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assert(typeof myGlobal != 'undefined');
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```
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`myGlobal`的值应为`10`。
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```js
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assert(myGlobal === 10);
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```
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应使用`var`关键字定义`myGlobal`。
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```js
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assert(/var\s+myGlobal/.test(code));
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```
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`oopsGlobal`应为全局变量且值为`5`。
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```js
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assert(typeof oopsGlobal != 'undefined' && oopsGlobal === 5);
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```
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# --seed--
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## --before-user-code--
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```js
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var logOutput = "";
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var originalConsole = console
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function capture() {
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var nativeLog = console.log;
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console.log = function (message) {
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logOutput = message;
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if(nativeLog.apply) {
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nativeLog.apply(originalConsole, arguments);
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} else {
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var nativeMsg = Array.prototype.slice.apply(arguments).join(' ');
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nativeLog(nativeMsg);
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}
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};
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}
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function uncapture() {
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console.log = originalConsole.log;
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}
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var oopsGlobal;
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capture();
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```
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## --after-user-code--
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```js
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fun1();
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fun2();
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uncapture();
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(function() { return logOutput || "console.log never called"; })();
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```
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## --seed-contents--
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```js
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// Declare the myGlobal variable below this line
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function fun1() {
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// Assign 5 to oopsGlobal Here
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}
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// Only change code above this line
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function fun2() {
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var output = "";
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if (typeof myGlobal != "undefined") {
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output += "myGlobal: " + myGlobal;
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}
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if (typeof oopsGlobal != "undefined") {
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output += " oopsGlobal: " + oopsGlobal;
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}
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console.log(output);
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}
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```
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# --solutions--
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```js
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var myGlobal = 10;
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function fun1() {
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oopsGlobal = 5;
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}
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function fun2() {
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var output = "";
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if(typeof myGlobal != "undefined") {
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output += "myGlobal: " + myGlobal;
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}
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if(typeof oopsGlobal != "undefined") {
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output += " oopsGlobal: " + oopsGlobal;
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}
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console.log(output);
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}
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```
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