Translating 1-js/05-data-types/09-destructuring-assignment #82
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@leviding 校对认领 |
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@lihanxiang ok |
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@leviding 校对认领 |
sunhaokk
reviewed
May 25, 2018
| @@ -148,45 +148,45 @@ let [firstName, surname] = []; | |||
| alert(firstName); // undefined | |||
| ``` | |||
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| If we want a "default" value to replace the missing one, we can provide it using `=`: | |||
| 如果我们想要提供一个“默认值”给缺失的变量，我们可以使用 `=` 来提供： | |||
| ``` | ||
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| Default values can be more complex expressions or even function calls. They are evaluated only if the value is not provided. | ||
| 默认值可以是更加复杂的表达式甚至可以是函数调用，这些表达式或函数只会在这个值缺失的时候才会被计算。 |
| @@ -204,16 +204,16 @@ alert(width); // 100 | |||
| alert(height); // 200 | |||
| ``` | |||
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| Properties `options.title`, `options.width` and `options.height` are assigned to the corresponding variables. The order does not matter. This works too: | |||
| 属性 `options.title`、`options.width` 和 `options.height` 的值被赋给了对应的变量。变量的顺序并不重要，以下的代码也奏效： | |||
| @@ -254,24 +254,25 @@ alert(width); // 100 | |||
| alert(height); // 200 | |||
| ``` | |||
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| Just like with arrays or function parameters, default values can be any expressions or even function calls. They will be evaluated if the value is not provided. | |||
| 就像数组或函数参数一样，默认值可以是表达式甚至是函数调用。只会在这个值缺失的时候才会被计算/调用。 | |||
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| The code below asks for width, but not the title. | |||
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| ```js run | ||
| let options = { | ||
| title: "Menu" | ||
| }; | ||
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| *!* | ||
| let {width = prompt("width?"), title = prompt("title?")} = options; | ||
| let {width = prompt("宽度?"), title = prompt("标题?")} = options; |
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此处并非代码，而是在生成的网站上与用户交互的提示语，为了全站统一，这里也让用户看到中文
| ````smart header="Gotcha without `let`" | ||
| In the examples above variables were declared right before the assignment: `let {…} = {…}`. Of course, we could use existing variables too. But there's a catch. | ||
| ````smart header="不使用 `let` 的疑难病症" | ||
| 在以上的例子中，变量都是在等号前才被声明的：`let {…} = {…}`。当然，我们也可以使用已有的变量。但这里有一个问题需要注意。 |
| let options = { | ||
| title: "My menu", | ||
| items: ["Item1", "Item2"] | ||
| }; | ||
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| // ...and it immediately expands it to variables | ||
| // ...然后函数马上把对象展开成变量 | ||
| function showMenu(*!*{title = "Untitled", width = 200, height = 100, items = []}*/!*) { | ||
| // title, items – taken from options, |
lihanxiang
reviewed
May 26, 2018
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| *Destructuring assignment* is a special syntax that allows us to "unpack" arrays or objects into a bunch of variables, as sometimes they are more convenient. Destructuring also works great with complex functions that have a lot of parameters, default values, and soon we'll see how these are handled too. | ||
| **解构赋值**是一种特殊的语法，它让我们可以将数组或对象进行“拆包”，存放到一系列的变量中，因为变量有时候更加方便。解构操作在那些具有很多参数和默认参数值的函数中也很奏效，很快我们就会看到这些都是怎么处理的。 |
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“因为变量有时候更加方便” => “因为有时候使用变量更加方便”
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| ```js | ||
| // we have an array with the name and surname | ||
| // 有一个存放了名字和姓氏数组 |
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“有一个存放了名字和姓氏数组” => “有一个存放了名字和姓氏的数组”
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| If there are fewer values in the array than variables in the assignment, there will be no error. Absent values are considered undefined: | ||
| 如果赋值语句中变量的数量多于数组中实际元素的数量，赋值不会报错。缺失的被当作 `undifined`： |
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@kezhenxu94 可以修改啦 |
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@leviding 修改完毕 |
leviding
approved these changes
May 27, 2018
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@leviding 翻译完成，resolve #65