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Co-authored-by: maoxiaoke <thebigyellowbee@qq.com> resolve #5
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校对认领 |
Starriers
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Apr 23, 2018
| **number** 类型用于整数和浮点数。 | ||
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| There are many operations for numbers, e.g. multiplication `*`, division `/`, addition `+`, subtraction `-` and so on. | ||
| 数字有很多操作，比如，乘法 `*`，除法 `/`，加法 `+`，减法 `-` 等等。 |
| The `typeof` operator allows us to see which type is stored in the variable. | ||
| - 两种形式： `typeof x` 或者 `typeof(x)`。 | ||
| - 返回的类型的字符串，比如 `"string"`。 | ||
| - `null` 返回 `"object"` -- 这是语言中的一个错误，实际上它并不是一个对象。 |
| - `number` 用于任何类型的数字： 整数或者浮点数。 | ||
| - `string` 用于字符串。一个字符串可以包含一个或多个字符，所以没有单独的单字符类型。 | ||
| - `boolean` 用于 `true` 和 `false`。 | ||
| - `null` 用于未知的值 -- 只有一个 `null` 值的独立类型。 |
| - `string` 用于字符串。一个字符串可以包含一个或多个字符，所以没有单独的单字符类型。 | ||
| - `boolean` 用于 `true` 和 `false`。 | ||
| - `null` 用于未知的值 -- 只有一个 `null` 值的独立类型。 | ||
| - `undefined` 用于未定义的值 -- 只有一个 `undefined` 值的独立类型。 |
| - `undefined` for unassigned values -- a standalone type that has a single value `undefined`. | ||
| - `object` for more complex data structures. | ||
| - `symbol` for unique identifiers. | ||
| `typeof` 运算符可以查看变量的类型。 |
| 2. The result of `typeof null` is `"object"`. That's wrong. It is an officially recognized error in `typeof`, kept for compatibility. Of course, `null` is not an object. It is a special value with a separate type of its own. So, again, that's an error in the language. | ||
| 3. The result of `typeof alert` is `"function"`, because `alert` is a function of the language. We'll study functions in the next chapters, and we'll see that there's no special "function" type in the language. Functions belong to the object type. But `typeof` treats them differently. Formally, it's incorrect, but very convenient in practice. | ||
| 1. `Math` 是一个提供数学运算的内建对象。我们会在章节 <info:number> 学习它。此处作为一个对象的例子。 | ||
| 2. `typeof null` 的结果是 `"object"`。这是不对的。这是一个官方承认的错误，为了兼容性而保留。当然，`null` 不是一个对象。它有自己的类型，是一个特殊值。再次强调，这是语言中的一个错误。 |
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这是一个官方承认的错误 =》这是官方在 typeof 方面承认的错误
| 2. `typeof null` 的结果是 `"object"`。这是不对的。这是一个官方承认的错误，为了兼容性而保留。当然，`null` 不是一个对象。它有自己的类型，是一个特殊值。再次强调，这是语言中的一个错误。 | ||
| 3. `typeof alert` 的结果是 `"function"`，因为 `alert` 在语言中是一个函数。我们会在下一章学习函数，那时我们会了解到，在语言中没有一个特别的 “function” 类型。函数隶属于 object 类型。但是 `typeof` 对函数区分对待。这不正确，但在实践中非常方便。 | ||
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| ## 总结 |
| `object` 类型是特殊的类型。 | ||
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| All other types are called "primitive", because their values can contain only a single thing (be it a string or a number or whatever). In contrast, objects are used to store collections of data and more complex entities. We'll deal with them later in the chapter <info:object> after we know enough about primitives. | ||
| 其他所有的类型都称为“原始类型”，因为它们的值只包含一个单独的东西（字符串、数字或者其他）。相反，对象用于储存数据集合和更复杂的实体。在充分了解原始类型之后，我们会在章节 <info:object> 介绍对象。 |
| 双引号和单引号都是“简单”引用，在 JavaScript 中两者并没有什么差别。 | ||
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| Backticks are "extended functionality" quotes. They allow us to embed variables and expressions into a string by wrapping them in `${…}`, for example: | ||
| 反引号是*功能扩展*的引用，允许通过`${…}`， 将变量和表达式嵌入到字符串中。例如： |
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功能扩展 用加粗方式
后面的 要空格
将 不要空格
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@leviding Done. |
leviding
approved these changes
Apr 24, 2018
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Co-authored-by: maoxiaoke thebigyellowbee@qq.com
Cc @maoxiaoke
resolve #5