99 lines
5.2 KiB
Markdown
99 lines
5.2 KiB
Markdown
# Template expression operators
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# 模板表达式运算符
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<div class="callout is-critical">
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<header>Marked for archiving</header>
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<header>已标记为归档</header>
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To ensure that you have the best experience possible, this topic is marked for archiving until we determine that it clearly conveys the most accurate information possible.
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为确保你拥有最佳的体验，本主题已标记为存档，直到我们确定其清楚地传达了最准确的信息为止。
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In the meantime, this topic might be helpful: [Hierarchical injectors](guide/hierarchical-dependency-injection).
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同时，下列主题可能会有所帮助：[分层注入器](guide/hierarchical-dependency-injection)。
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If you think this content should not be archived, please file a [GitHub issue](https://github.com/angular/angular/issues/new?template=3-docs-bug.md).
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如果你认为不应将此内容存档，请提交 [GitHub 问题](https://github.com/angular/angular/issues/new?template=3-docs-bug.md)。
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</div>
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The Angular template expression language employs a subset of JavaScript syntax supplemented with a few special operators
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for specific scenarios.
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Angular 模板表达语言采用了 JavaScript 语法的子集，并为特定情况添加了一些特殊的运算符。
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<div class="alert is-helpful">
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See the <live-example></live-example> for a working example containing the code snippets in this guide.
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有关包含本指南中代码片段的有效示例，请参见<live-example></live-example>
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</div>
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{@a non-null-assertion-operator}
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## The non-null assertion operator ( `!` )
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## 非空断言运算符（ `!` ）
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When you use TypeScript's `--strictNullChecks` flag, you can prevent the type checker from throwing an error with Angular's non-null assertion operator, `!`.
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使用 TypeScript 的 `--strictNullChecks` 标志时，可以防止类型检查器使用 Angular 的非空断言运算符 `!` 。
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The Angular non-null assertion operator causes the TypeScript type checker to suspend strict `null` and `undefined` checks for a specific property expression.
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Angular 非空断言运算符使 TypeScript 类型检查器暂停对特定属性表达式的 `null` 和 `undefined` 的严格检查。
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For example, you can assert that `item` properties are also defined.
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例如，你可以断言 `item` 也是已定义的。
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<code-example path="template-expression-operators/src/app/app.component.html" region="non-null" header="src/app/app.component.html"></code-example>
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Often, you want to make sure that any property bindings aren't `null` or `undefined`.
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However, there are situations in which such states are acceptable.
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For those situations, you can use Angular's non-null assertion operator to prevent TypeScript from reporting that a property is `null` or `undefined`.
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通常，你要确保任何属性绑定都不为 `null` 或 `undefined` 。但是，在某些情况下，这种状态是可以接受的。对于这些情况，可以使用 Angular 的非空断言运算符来防止 TypeScript 报告某个属性为 `null` 或 `undefined`。
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The non-null assertion operator, `!`, is optional unless you turn on strict null checks.
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非空断言运算符 `!` 是可选的，除非你要启用严格的空检查。
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For more information, see TypeScript's [strict null checking](http://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html "Strict null checking in TypeScript").
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有关更多信息，请参见 TypeScript 的[严格空检查](http://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html "TypeScript 中严格的 null 检查")。
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{@a any-type-cast-function}
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## The `$any()` type cast function
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## `$any()` 类型转换函数
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Sometimes a binding expression triggers a type error during [AOT compilation](guide/aot-compiler) and it is not possible or difficult to fully specify the type.
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To silence the error, you can use the `$any()` cast function to cast
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the expression to the [`any` type](https://www.typescriptlang.org/docs/handbook/basic-types.html#any) as in the following example:
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有时，绑定表达式会在 [AOT 编译](guide/aot-compiler)期间触发类型错误，并且不可能或很难完全指定类型。要使此错误静音，可以使用 `$any()` 强制转换函数把表达式强制转换为 [`any` 类型](https://www.typescriptlang.org/docs/handbook/basic-types.html#any)，如下例所示：
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<code-example path="built-in-template-functions/src/app/app.component.html" region="any-type-cast-function-1" header="src/app/app.component.html"></code-example>
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Using `$any()` prevents TypeScript from reporting that `bestByDate` is not a member of the `item` object.
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使用 `$any()` 可以防止 TypeScript 报告 `bestByDate` 不是 `item` 对象成员的错误。
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The `$any()` cast function also works with `this` to allow access to undeclared members of the component.
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`$any()` 强制转换函数也可以与 `this` 一起使用，以允许访问组件的未声明成员。
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<code-example path="built-in-template-functions/src/app/app.component.html" region="any-type-cast-function-2" header="src/app/app.component.html"></code-example>
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The `$any()` cast function works anywhere in a binding expression where a method call is valid.
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`$any()` 强制转换函数可在绑定表达式中任何进行方法调用的地方使用。
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