在自定义 HTML 元素上定义多个自定义属性

Defining multiple custom attributes on a custom HTML Element

为自定义 HTML 元素的自定义属性添加 getter/setter 非常简单:

  customElements.define('custom-el', class extends HTMLElement {
    
    static get observedAttributes() {
      return ['customAttr']
    }

    get customAttr() {
      return this.getAttribute('customAttr')
    }

    set customAttr(value) {
      this.setAttribute('customAttr', value)
    }

    constructor() {
      super();
    }
    
  })

但是,如果您在同一个元素上有多个自定义属性,这会变得非常麻烦:

  customElements.define('custom-el', class extends HTMLElement {
    
    static get observedAttributes() {
      return ['customAttr1', 'customAttr2', 'customAttr3']
    }

    // for attr 1

    get customAttr1() {
      return this.getAttribute('customAttr1')
    }

    set customAttr1(value) {
      this.setAttribute('customAttr1', value)
    }

    // for attr 2

    get customAttr2() {
      return this.getAttribute('customAttr2')
    }

    set customAttr2(value) {
      this.setAttribute('customAttr2', value)
    }

    // for attr 3

    get customAttr3() {
      return this.getAttribute('customAttr3')
    }

    set customAttr3(value) {
      this.setAttribute('customAttr3', value)
    }

    constructor() {
      super();
    }
    
  })

我一直在考虑如何编写一个函数来从自定义属性名称数组生成 getter/setters,但是如果不能将变量字符串作为get/set.

的名称

documentation for "getter"建议方括号中的表达式是可以接受的,这适用于一个可变字符串:

const x = "customAttr";

customElements.define('custom-el', class extends HTMLElement {
    
  static get observedAttributes() {
    return x;
  }

  get [x]() {
    return this.getAttribute(x)
  }

  set [x](value) {
    this.setAttribute(x, value)
  }

  constructor() {
    super(); 
  }

})
<custom-el customAttr="It works"></custom-el>
console.log(document.querySelector("custom-el").customAttr) // yields "It works"

不幸的是,for/forEach 循环在自定义元素定义的主体中是不允许的(在嵌入式子例程之外,此时 get/set 操作不再有效!):

const customAttrs = ["customAttr1", "customAttr2", "customAttr3"];

customElements.define('custom-el', class extends HTMLElement {
    
  static get observedAttributes() {
    return customAttrs;
  }

  customAttrs.forEach( customAttr => {
    get [customAttr]() {
      return this.getAttribute(customAttr)
    }

    set [customAttr](value) {
      this.setAttribute(customAttr, value)
    }
  })

  constructor() {
    super(); 
  }

})
<custom-el customAttr1="It " customAttr2="doesn't " customAttr3="work"></custom-el>
let customEl = document.querySelector("custom-el");
console.log(testEl.customAttr1+testEl.customAttr2+testEl.customAttr3) // yields error

如果自定义 HTMLElement class 有一个像对象的“defineProperty”一样操作的“defineAttribute”方法,你可以这样做:

const customEl = ...

const customAttrs = ["customAttr1", "customAttr2", "customAttr3", ...]

customAttrs.forEach( customAttr => {
  HTMLElement.defineAttribute(customEl, customAttr, {
    get : function(){ return this.getAttribute(customAttr ); },
    set : function(newValue){ this.setAttribute(customAttr, newValue); }
  }
}

...但似乎不存在这样的东西。

tl;dr - 在自定义元素上为自定义属性设置多个 setter/getters 真的没有比为每个属性编写 set/get 定义更好的方法了吗?

使用Object.defineProperty( element , attrName , { getter , setter , options} )

类似的内容添加到您的基类(因此this是您的自定义元素)

  defineProperty(
    attr,
    getter = (attr) => this.getAttribute(attr),
    setter = (val, attr) => (val == undefined ? this.removeAttribute(attr) : this.setAttribute(attr, val)),
    options = {
      configurable: true,
    }
  ) {
    return Object.defineProperty(this, attr, {
      get() {
        return getter(attr);
      },
      set(val) {
        return setter(val, attr);
      },
      ...options,
    });
  }

参见:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

复数:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperties