Skip to main content

@babel/plugin-proposal-do-expressions

详情​

¥Detail

do { .. } 表达式执行一个块（其中包含一条或多条语句），块内的最终语句完成值成为 do 表达式的完成值。

¥The do { .. } expression executes a block (with one or many statements in it), and the final statement completion value inside the block becomes the completion value of the do expression.

来自 你不知道的 JS, Types & Grammar -> Chapter 5 -> Section Statement Completion Values

¥from You Don't Know JS, Types & Grammar -> Chapter 5 -> Section Statement Completion Values

可以看成是 三元运算符 的复杂版本：

¥It can be seen as a complex version of the ternary operator:

JavaScript
let a = do {
  if (x > 10) {
    ("big");
  } else {
    ("small");
  }
};
// is equivalent to:
let a = x > 10 ? "big" : "small";

这个例子不是最好的用法，因为它太简单了，使用三元运算符是一个更好的选择，但是你可以在 do { ... } 表达式中使用多个 if ... else 链的更复杂的条件：

¥This example is not the best usage because it is too simple and using a ternary operator is a better option but you can have a much more complex condition in the do { ... } expression with several if ... else chains:

JavaScript
let x = 100;
let y = 20;

let a = do {
  if (x > 10) {
    if (y > 20) {
      ("big x, big y");
    } else {
      ("big x, small y");
    }
  } else {
    if (y > 10) {
      ("small x, big y");
    } else {
      ("small x, small y");
    }
  }
};

示例​

¥Example

在 JSX 中​

¥In JSX

do 表达式最有用的用法之一是在 JSX 内部。如果我们想有条件地显示一个组件，我们通常必须调用另一个函数来实现条件并返回正确的值，例如：

¥One of the most useful usage of the do expression is inside JSX. If we want to conditionally display a component we usually have to call another function which would implement the condition and return the correct value, for example:

JavaScript
const getColoredComponent = color => {
  if (color === "blue") {
    return <BlueComponent />;
  }
  if (color === "red") {
    return <RedComponent />;
  }
  if (color === "green") {
    return <GreenComponent />;
  }
};

const Component = props => (
  <div className="myComponent">{getColoredComponent()}</div>
);

使用 do 表达式，你可以在 JSX 中添加逻辑：

¥Using a do expression you can add logic inside JSX:

JavaScript
const Component = props => (
  <div className="myComponent">
    {do {
      if (color === "blue") {
        <BlueComponent />;
      } else if (color === "red") {
        <RedComponent />;
      } else if (color === "green") {
        <GreenComponent />;
      }
    }}
  </div>
);

安装​

¥Installation

npm install --save-dev @babel/plugin-proposal-do-expressions

用法​

¥Usage

¥With a configuration file (Recommended)

babel.config.json
{
  "plugins": ["@babel/plugin-proposal-do-expressions"]
}

通过 CLI​

¥Via CLI

Shell
babel --plugins @babel/plugin-proposal-do-expressions script.js

通过 Node API​

¥Via Node API

JavaScript
require("@babel/core").transformSync("code", {
  plugins: ["@babel/plugin-proposal-do-expressions"],
});

参考​

¥References