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@babel/plugin-transform-class-properties

info

This plugin is included in @babel/preset-env, in ES2022

Example​

示例​

以下展示了一个包含 4 个属性的类，它们将会被转译。

JavaScript
class Bork {
  //Property initializer syntax
  instanceProperty = "bork";
  boundFunction = () => {
    return this.instanceProperty;
  };

    // 静态类属性
    static staticProperty = "babelIsCool";
    static staticFunction = function() {
      return Bork.staticProperty;
    };
  }

  let myBork = new Bork;

  // 属性初始化器设定的值不在原型上
  console.log(myBork.__proto__.boundFunction); // > undefined

  // 绑定函数绑定到类实例上
  console.log(myBork.boundFunction.call(undefined)); // > "bork"

  // 类上包含静态函数
  console.log(Bork.staticFunction()); // > "babelIsCool"

安装​

npm install --save-dev @babel/plugin-transform-class-properties

用法​

使用配置文件（推荐）​

未使用选项：

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

使用选项：

babel.config.json
{
  "plugins": [["@babel/plugin-transform-class-properties", { "loose": true }]]
}

通过 CLI 使用​

Shell
babel --plugins @babel/plugin-transform-class-properties script.js

通过 Node API 使用​

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

选项​

loose​

boolean，默认为 false。

当设置为 true 时，类属性将被编译为赋值表达式而不是 Object.defineProperty。

caution

Consider migrating to the top level setPublicClassFields assumption

babel.config.json
{
  "assumptions": {
    "setPublicClassFields": true
  }
}

有关使用其中任何一种结果的解释，请参考 Definition vs. Assignment (第 5 部分为总结)

示例​

JavaScript
class Bork {
  static a = "foo";
  static b;

  x = "bar";
  y;
}

When setPublicClassFields is false, the above code will compile to the following, using Object.defineProperty:

JavaScript
var Bork = function Bork() {
  babelHelpers.classCallCheck(this, Bork);
  Object.defineProperty(this, "x", {
    configurable: true,
    enumerable: true,
    writable: true,
    value: "bar",
  });
  Object.defineProperty(this, "y", {
    configurable: true,
    enumerable: true,
    writable: true,
    value: void 0,
  });
};

Object.defineProperty(Bork, "a", {
  configurable: true,
  enumerable: true,
  writable: true,
  value: "foo",
});
Object.defineProperty(Bork, "b", {
  configurable: true,
  enumerable: true,
  writable: true,
  value: void 0,
});

When setPublicClassFields is set to true, it will compile using assignment expressions:

JavaScript
var Bork = function Bork() {
  babelHelpers.classCallCheck(this, Bork);
  this.x = "bar";
  this.y = void 0;
};

Bork.a = "foo";
Bork.b = void 0;
tip

You can read more about configuring plugin options here

参考​