babel装饰器和TypeScript一样吗？

Question

我使用TypeScript进行了很多编码,但不太熟悉,我知道TypeScript如何在装饰器上工作,而babel也支持装饰器,它们的行为是否相同？

Answer 1

是的,它们是相同的,在某种意义上它们产生相同的行为,但它们具有不同的实现.

两者都遵循ECMAScript规范并尽早为我们带来功能.您可以预期,未来节点或浏览器可能会支持它们上的内容.

码:

function f() {
  console.log("f(): evaluated");
  return function (target, propertyKey, descriptor) {
      console.log("f(): called");
  }
}

function g() {
  console.log("g(): evaluated");
  return function (target, propertyKey, descriptor) {
      console.log("g(): called");
  }
}

class C {
  @f()
  @g()
  method() {}
}

new C().method();

TypeScript输出:

var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
    return c > 3 && r && Object.defineProperty(target, key, r), r;
};
function f() {
    console.log("f(): evaluated");
    return function (target, propertyKey, descriptor) {
        console.log("f(): called");
    };
}
function g() {
    console.log("g(): evaluated");
    return function (target, propertyKey, descriptor) {
        console.log("g(): called");
    };
}
class C {
    method() { }
}
__decorate([
    f(),
    g()
], C.prototype, "method", null);
new C().method();

通天输出:

"use strict";

var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();

var _dec, _dec2, _desc, _value, _class;

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

function _applyDecoratedDescriptor(target, property, decorators, descriptor, context) {
  var desc = {};
  Object['ke' + 'ys'](descriptor).forEach(function (key) {
    desc[key] = descriptor[key];
  });
  desc.enumerable = !!desc.enumerable;
  desc.configurable = !!desc.configurable;

  if ('value' in desc || desc.initializer) {
    desc.writable = true;
  }

  desc = decorators.slice().reverse().reduce(function (desc, decorator) {
    return decorator(target, property, desc) || desc;
  }, desc);

  if (context && desc.initializer !== void 0) {
    desc.value = desc.initializer ? desc.initializer.call(context) : void 0;
    desc.initializer = undefined;
  }

  if (desc.initializer === void 0) {
    Object['define' + 'Property'](target, property, desc);
    desc = null;
  }

  return desc;
}

function f() {
  console.log("f(): evaluated");
  return function (target, propertyKey, descriptor) {
    console.log("f(): called");
  };
}

function g() {
  console.log("g(): evaluated");
  return function (target, propertyKey, descriptor) {
    console.log("g(): called");
  };
}

var C = (_dec = f(), _dec2 = g(), (_class = function () {
  function C() {
    _classCallCheck(this, C);
  }

  _createClass(C, [{
    key: "method",
    value: function method() {}
  }]);

  return C;
}(), (_applyDecoratedDescriptor(_class.prototype, "method", [_dec, _dec2], Object.getOwnPropertyDescriptor(_class.prototype, "method"), _class.prototype)), _class));


new C().method();

运行后输出:

> ts-node ts-example.ts
f(): evaluated
g(): evaluated
g(): called
f(): called

> node babel-example.js
f(): evaluated
g(): evaluated
g(): called
f(): called