Skip to main content

@babel/plugin-transform-block-scoping

info

这个插件包含在 @babel/preset-env 中

示例​

🌐 Examples

在

JavaScript
{
  let a = 3;
}

let a = 3;

出

JavaScript
{
  var _a = 3;
}

var a = 3;

不断检查​

🌐 Constant checks

这个插件还会验证所有 const 变量。重新分配常量是运行时错误，它会为这些插入必要的错误代码。

🌐 This plugin also validates all const variables. Reassignment of constants is a runtime error and it will insert the necessary error code for those.

安装​

🌐 Installation

npm install --save-dev @babel/plugin-transform-block-scoping

用法​

🌐 Usage

🌐 With a configuration file (Recommended)

没有选项：

🌐 Without options:

babel.config.json
{
  "plugins": ["@babel/plugin-transform-block-scoping"]
}

有选项：

🌐 With options:

babel.config.json
{
  "plugins": [
    [
      "@babel/plugin-transform-block-scoping",
      {
        "throwIfClosureRequired": true
      }
    ]
  ]
}

通过 CLI​

🌐 Via CLI

Shell
babel --plugins @babel/plugin-transform-block-scoping script.js

通过 Node API​

🌐 Via Node API

JavaScript
require("@babel/core").transformSync("code", {
  plugins: ["@babel/plugin-transform-block-scoping"],
});

选项​

🌐 Options

throwIfClosureRequired​

boolean，默认值为 false。

在以下情况下，如果在转换时不添加额外的函数和闭包，就不可能重写 let/const：

🌐 In cases such as the following it's impossible to rewrite let/const without adding an additional function and closure while transforming:

JavaScript
for (let i = 0; i < 5; i++) {
  setTimeout(() => console.log(i), 1);
}

在对性能特别敏感的代码中，这可能是不理想的。如果设置了 "throwIfClosureRequired": true，Babel 在转换这些模式时会抛出错误，而不是自动添加一个额外的函数。

🌐 In extremely performance-sensitive code, this can be undesirable. If "throwIfClosureRequired": true is set, Babel throws when transforming these patterns instead of automatically adding an additional function.

tdz​

boolean，默认值为 false。

默认情况下，这个插件会忽略块级作用域变量的 暂时性死区 (TDZ)。以下代码在用 Babel 转译时不会报错，这并不符合规范：

🌐 By default this plugin will ignore the temporal dead zone (TDZ) for block-scoped variables. The following code will not throw an error when transpiled with Babel, which is not spec compliant:

JavaScript
i;
let i;

如果你需要这些错误，你可以通过为这个插件设置 "tdz": true 来让 Babel 尝试找到它们。不过，目前的实现可能无法处理所有边缘情况，最好一开始就避免写这样的代码。

🌐 If you need these errors you can tell Babel to try and find them by setting "tdz": true for this plugin. However, the current implementation might not get all edge cases right and its best to just avoid code like this in the first place.

tip

你可以在这里了解更多关于配置插件选项的内容