[英]Extending Built-in Array With ES6 Classes - Method is not a function error
我正在嘗試擴展內置數組 class 並創建基於自定義 collections 的本機數組 class。
我可以使用自定義名稱創建集合,效果很好,但我不能使用我的自定義方法。 如果我使用 findAnimal 方法,它給我method is not a function
錯誤。 如果我記錄收集並檢查原型,我將看不到我的自定義方法。
我意識到我將代碼轉換為 es5,如果我沒有,效果很好,ts 編譯器的 es5 降級代碼會出現問題。
如果我們使用 babel 將代碼降級為 es5,轉譯后的代碼效果很好。 ts 編譯器在轉譯代碼時遺漏了一些東西,或者我遺漏了一些重要的配置。
interface Animal {
name: string;
weight: number
}
class AnimalCollection extends Array <Animal> {
constructor(name, ...items) {
super(...items);
Object.defineProperty(this, 'name', {
enumerable: false,
writable: false,
value: name
})
}
findAnimal(name): Animal {
return this.find(a => a.name === name) || null;
}
}
const animalsArray = [
{name: 'TD-23', weight: 60},
{name: 'TD-25', weight: 50},
{name: 'TXD-26', weight: 120},
{name: 'TYD-26', weight: 40}
];
const animals = new AnimalCollection('Deers', ...animalsArray)
console.log(animals.findAnimal('TD-23'));
// Uncaught TypeError: animals.findAnimal is not a function
ES5 降級
var __extends = (this && this.__extends) || (function () {
var extendStatics = function (d, b) {
extendStatics = Object.setPrototypeOf ||
({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
return extendStatics(d, b);
};
return function (d, b) {
extendStatics(d, b);
function __() { this.constructor = d; }
d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
})();
var __spreadArrays = (this && this.__spreadArrays) || function () {
for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
for (var r = Array(s), k = 0, i = 0; i < il; i++)
for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++)
r[k] = a[j];
return r;
};
var AnimalCollection = /** @class */ (function (_super) {
__extends(AnimalCollection, _super);
function AnimalCollection(name) {
var items = [];
for (var _i = 1; _i < arguments.length; _i++) {
items[_i - 1] = arguments[_i];
}
var _this = _super.apply(this, items) || this;
Object.defineProperty(_this, 'name', {
enumerable: false,
writable: false,
value: name
});
return _this;
}
AnimalCollection.prototype.findAnimal = function (name) {
return this.find(function (a) { return a.name === name; }) || null;
};
return AnimalCollection;
}(Array));
var animalsArray = [
{ name: 'TD-23', weight: 60 },
{ name: 'TD-25', weight: 50 },
{ name: 'TXD-26', weight: 120 },
{ name: 'TYD-26', weight: 40 }
];
var animals = new (AnimalCollection.bind.apply(AnimalCollection, __spreadArrays([void 0, 'Deers'], animalsArray)))();
console.log(animals.findAnimal('TD-23'));
為了回答您修改后的問題,TypeScript 不允許您擴展內置函數,如Array
、 Error
等。原因寫在這里。
在 ES2015 中,返回 object 的構造函數隱式地將 this 的值替換為 super(...) 的任何調用者。 生成的構造函數代碼必須捕獲 super(...) 的任何潛在返回值並將其替換為 this。
因此,子類化 Error、Array 和其他可能不再按預期工作。 這是因為 Error、Array 等的構造函數使用 ECMAScript 6 的 new.target 來調整原型鏈; 但是,在 ECMAScript 5 中調用構造函數時,無法確保 new.target 的值。其他低級編譯器默認情況下通常具有相同的限制。
所以如果你必須在 ES5 環境下擴展內置的Array
,那么你可以嘗試 Babel 來編譯你的代碼。 但是請注意,它有此處所述的限制。
由於 ES5 中的限制(對於 transform-classes 插件),無法正確子類化諸如 Date、Array、DOM 等內置類。 您可以嘗試使用基於 Object.setPrototypeOf 和 Reflect.construct 的 babel-plugin-transform-builtin-extend,但它也有一些限制。
雖然代碼本身可以完美找到並且在瀏覽器中也可以正常執行,但我認為您遇到的錯誤是由於 TypeScript 編譯器造成的。
對於源代碼
interface Animal {
name: string;
weight: number
}
class AnimalCollection extends Array <Animal> {
constructor(name: string, ...items: Animal[]) {
super(...items);
Object.defineProperty(this, 'name', {
enumerable: false,
writable: false,
value: name
})
}
findAnimal(name:string): Animal | null {
return this.find(a => a.name === name) || null;
}
}
const animalsArray = [
{name: 'TD-23', weight: 60},
{name: 'TD-25', weight: 50},
{name: 'TXD-26', weight: 120},
{name: 'TYD-26', weight: 40}
];
const animals = new AnimalCollection('Deers', ...animalsArray)
console.log(animals.findAnimal('TD-23'));
如果編譯器目標選項設置為ES5
,那么它會生成破壞實現的代碼。 它生成的代碼是
"use strict";
var __extends = (this && this.__extends) || (function () {
var extendStatics = function (d, b) {
extendStatics = Object.setPrototypeOf ||
({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
return extendStatics(d, b);
};
return function (d, b) {
extendStatics(d, b);
function __() { this.constructor = d; }
d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
})();
var __spreadArrays = (this && this.__spreadArrays) || function () {
for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
for (var r = Array(s), k = 0, i = 0; i < il; i++)
for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++)
r[k] = a[j];
return r;
};
var AnimalCollection = /** @class */ (function (_super) {
__extends(AnimalCollection, _super);
function AnimalCollection(name) {
var items = [];
for (var _i = 1; _i < arguments.length; _i++) {
items[_i - 1] = arguments[_i];
}
var _this = _super.apply(this, items) || this;
Object.defineProperty(_this, 'name', {
enumerable: false,
writable: false,
value: name
});
return _this;
}
AnimalCollection.prototype.findAnimal = function (name) {
return this.find(function (a) { return a.name === name; }) || null;
};
return AnimalCollection;
}(Array));
var animalsArray = [
{ name: 'TD-23', weight: 60 },
{ name: 'TD-25', weight: 50 },
{ name: 'TXD-26', weight: 120 },
{ name: 'TYD-26', weight: 40 }
];
var animals = new (AnimalCollection.bind.apply(AnimalCollection, __spreadArrays([void 0, 'Deers'], animalsArray)))();
console.log(animals.findAnimal('TD-23'));
但是,如果我們將tsconfig.json
中的target
設置為等於或大於ES2015
,那么它生成的代碼是
"use strict";
class AnimalCollection extends Array {
constructor(name, ...items) {
super(...items);
Object.defineProperty(this, 'name', {
enumerable: false,
writable: false,
value: name
});
}
findAnimal(name) {
return this.find(a => a.name === name) || null;
}
}
const animalsArray = [
{ name: 'TD-23', weight: 60 },
{ name: 'TD-25', weight: 50 },
{ name: 'TXD-26', weight: 120 },
{ name: 'TYD-26', weight: 40 }
];
const animals = new AnimalCollection('Deers', ...animalsArray);
console.log(animals.findAnimal('TD-23'));
這當然有效。 所以我認為 ES5 或更低版本的 TypeScript 編譯器存在問題,這會破壞實現。 我嘗試使用Babel 進行編譯,它適用於 ES5。
我可以看到您缺少一些any
,這是對我有用的代碼:
interface Animal {
name: string;
weight: number
}
class AnimalCollection extends Array <Animal> {
constructor(name: string, ...items : Array <Animal>) { // <-- missing types
super(...items);
Object.defineProperty(this, 'name', {
enumerable: false,
writable: false,
value: name
})
}
findAnimal(name : any): Animal|null { // <-- missing null
return this.find(a => a.name === name) || null;
}
}
const animalsArray = [
{name: 'TD-23', weight: 60},
{name: 'TD-25', weight: 50},
{name: 'TXD-26', weight: 120},
{name: 'TYD-26', weight: 40}
];
const animals = new AnimalCollection('Deers', ...animalsArray)
console.log(animals.findAnimal('TD-23'));
但是,此代碼生成以下 JS:
"use strict";
class AnimalCollection extends Array {
constructor(name, ...items) {
super(...items);
Object.defineProperty(this, 'name', {
enumerable: false,
writable: false,
value: name
});
}
findAnimal(name) {
return this.find(a => a.name === name) || null;
}
}
const animalsArray = [
{ name: 'TD-23', weight: 60 },
{ name: 'TD-25', weight: 50 },
{ name: 'TXD-26', weight: 120 },
{ name: 'TYD-26', weight: 40 }
];
const animals = new AnimalCollection('Deers', ...animalsArray);
console.log(animals.findAnimal('TD-23'));
不會產生任何錯誤
這是您編寫 function 的方式導致錯誤
interface Animal { name: string; weight: number } class AnimalCollection extends Array <Animal> { constructor(name, ...items) { super(...items); Object.defineProperty(this, 'name', { enumerable: false, writable: false, value: name }) } findAnimal:Animal=(name:String)=> { return this.find(a => a.name === name) || null; } } const animalsArray = [ {name: 'TD-23', weight: 60}, {name: 'TD-25', weight: 50}, {name: 'TXD-26', weight: 120}, {name: 'TYD-26', weight: 40} ]; const animals = new AnimalCollection('Deers', ...animalsArray) console.log(animals.findAnimal('TD-23')); // Uncaught TypeError: animals.findAnimal is not a function
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