内置指令

@customElement('my-element')
class MyElement extends LitElement {

  @property({type: Boolean})
  enabled = false;

  render() {
    const classes = { enabled: this.enabled, hidden: false };
    return html`<div class=${classMap(classes)}>Classy text</div>`;
  }
}

class MyElement extends LitElement {
  static properties = {
    enabled: {type: Boolean},
  };

  constructor() {
    super();
    this.enabled = false;
  }

  render() {
    const classes = { enabled: this.enabled, hidden: false };
    return html`<div class=${classMap(classes)}>Classy text</div>`;
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  @property({type: Boolean})
  enabled = false;

  render() {
    const styles = { backgroundColor: this.enabled ? 'blue' : 'gray', color: 'white' };
    return html`<p style=${styleMap(styles)}>Hello style!</p>`;
  }
}

class MyElement extends LitElement {
  static properties = {
    enabled: {type: Boolean},
  };

  constructor() {
    super();
    this.enabled = false;
  }

  render() {
    const styles = { backgroundColor: this.enabled ? 'blue' : 'gray', color: 'white' };
    return html`<p style=${styleMap(styles)}>Hello style!</p>`;
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  @property()
  items: Array<{id: number, name: string}> = [];

  render() {
    return html`
      <ul>
        ${repeat(this.items, (item) => item.id, (item, index) => html`
          <li>${index}: ${item.name}</li>`)}
      </ul>
    `;
  }
}

class MyElement extends LitElement {
  static properties = {
    items: {},
  };

  constructor() {
    super();
    this.items = [];
  }

  render() {
    return html`
      <ul>
        ${repeat(this.items, (item) => item.id, (item, index) => html`
          <li>${index}: ${item.name}</li>`)}
      </ul>
    `;
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  @property()
  filename: string | undefined = undefined;

  @property()
  size: string | undefined = undefined;

  render() {
    // 如果 size 或 filename 未定义，则不渲染 src 属性
    return html`<img src="/images/${ifDefined(this.size)}/${ifDefined(this.filename)}">`;
  }
}

class MyElement extends LitElement {
  static properties = {
    filename: {},
    size: {},
  };

  constructor() {
    super();
    this.filename = undefined;
    this.size = undefined;
  }

  render() {
    // 如果 size 或 filename 未定义，则不渲染 src 属性
    return html`<img src="/images/${ifDefined(this.size)}/${ifDefined(this.filename)}">`;
  }
}
customElements.define('my-element', MyEleent);

const detailView = (data) => html`<div>...</div>`;
const summaryView = (data) => html`<div>...</div>`;

@customElement('my-element')
class MyElement extends LitElement {

  @property()
  data = {showDetails: true, /*...*/ };

  render() {
    return html`${cache(this.data.showDetails
      ? detailView(this.data)
      : summaryView(this.data)
    )}`;
  }
}

const detailView = (data) => html`<div>...</div>`;
const summaryView = (data) => html`<div>...</div>`;

class MyElement extends LitElement {
  static properties = {
    data: {},
  };

  constructor() {
    super();
    this.data = {showDetails: true, /*...*/ };
  }

  render() {
    return html`${cache(this.data.showDetails
      ? detailView(this.data)
      : summaryView(this.data)
    )}`;
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  @property()
  userId: string = '';

  render() {
    return html`
      <div>
        ${keyed(this.userId, html`<user-card .userId=${this.userId}></user-card>`)}
      </div>`;
  }
}

class MyElement extends LitElement {
  static properties = {
    userId: {},
  };

  constructor() {
    super();
    this.userId = '';
  }

  render() {
    return html`
      <div>
        ${keyed(this.userId, html`<user-card .userId=${this.userId}></user-card>`)}
      </div>`;
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  @property()
  value: string = '';

  render() {
    return html`
      <div>
        ${guard([this.value], () => calculateSHA(this.value))}
      </div>`;
  }
}

class MyElement extends LitElement {
  static properties = {
    value: {},
  };

  constructor() {
    super();
    this.value = '';
  }

  render() {
    return html`
      <div>
        ${guard([this.value], () => calculateSHA(this.value))}
      </div>`;
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  @property()
  data = {value: 'test'};

  render() {
    return html`<input .value=${live(this.data.value)}>`;
  }
}

class MyElement extends LitElement {
  static properties = {
    data: {},
  };

  constructor() {
    super();
    this.data = {value: 'test'};
  }

  render() {
    return html`<input .value=${live(this.data.value)}>`;
  }
}
customElements.define('my-element', MyElement);

const templateEl = document.querySelector('template#myContent') as HTMLTemplateElement;

@customElement('my-element')
class MyElement extends LitElement {

  render() {
    return  html`
      这里是来自模板元素的一些内容：
      ${templateContent(templateEl)}`;
  }
}

const templateEl = document.querySelector('template#myContent');

class MyElement extends LitElement {

  render() {
    return  html`
      这里是来自模板元素的一些内容：
      ${templateContent(templateEl)}`;
  }
}
customElements.define('my-element', MyElement);

const markup = '<h3>Some HTML to render.</h3>';

@customElement('my-element')
class MyElement extends LitElement {

  render() {
    return html`
      注意，潜在不安全的 HTML 内容：
      ${unsafeHTML(markup)}
    `;
  }
}

const markup = '<h3>Some HTML to render.</h3>';

class MyElement extends LitElement {

  render() {
    return html`
      注意，潜在不安全的 HTML 内容：
      ${unsafeHTML(markup)}
    `;
  }
}
customElements.define('my-element', MyElement);

const svg = '<circle cx="50" cy="50" r="40" fill="red" />';

@customElement('my-element')
class MyElement extends LitElement {

  render() {
    return html`
      注意，潜在不安全的 SVG 内容：
      <svg width="40" height="40" viewBox="0 0 100 100"
        xmlns="http://www.w3.org/2000/svg" version="1.1">
        ${unsafeSVG(svg)}
      </svg> `;
  }
}

const svg = '<circle cx="50" cy="50" r="40" fill="red" />';

class MyElement extends LitElement {

  render() {
    return html`
      注意，潜在不安全的 SVG 内容：
      <svg width="40" height="40" viewBox="0 0 100 100"
        xmlns="http://www.w3.org/2000/svg" version="1.1">
        ${unsafeSVG(svg)}
      </svg> `;
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  inputRef: Ref<HTMLInputElement> = createRef();

  render() {
    // 将 ref 指令传递给一个将在 .value 中保存元素的 Ref 对象
    return html`<input ${ref(this.inputRef)}>`;
  }

  firstUpdated() {
    const input = this.inputRef.value!;
    input.focus();
  }
}

class MyElement extends LitElement {

  inputRef = createRef();

  render() {
    // 将 ref 指令传递给一个将在 .value 中保存元素的 Ref 对象
    return html`<input ${ref(this.inputRef)}>`;
  }

  firstUpdated() {
    const input = this.inputRef.value!;
    input.focus();
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  render() {
    // 将 ref 指令传递给变更回调
    return html`<input ${ref(this.inputChanged)}>`;
  }

  inputChanged(input?: HTMLInputElement) {
    input?.focus();
  }
}

class MyElement extends LitElement {

  render() {
    // 将 ref 指令传递给变更回调
    return html`<input ${ref(this.inputChanged)}>`;
  }

  inputChanged(input) {
    input?.focus();
  }
}
customElements.define('my-element', MyElement);

@customElement('my-element')
class MyElement extends LitElement {

  @state()
  private content = fetch('./content.txt').then(r => r.text());

  render() {
    return html`${until(this.content, html`<span>加载中...</span>`)}`;
  }
}

class MyElement extends LitElement {
  static properties = {
    content: {state: true},
  };

  constructor() {
    super();
    this.content = fetch('./content.txt').then(r => r.text());
  }

  render() {
    return html`${until(this.content, html`<span>加载中...</span>`)}`;
  }
}
customElements.define('my-element', MyElement);

async function *tossCoins(count: number) {
  for (let i=0; i<count; i++) {
    yield Math.random() > 0.5 ? '正面' : '反面';
    await new Promise((r) => setTimeout(r, 1000));
  }
}

@customElement('my-element')
class MyElement extends LitElement {

  @state()
  private tosses = tossCoins(10);

  render() {
    return html`
      <ul>${asyncAppend(this.tosses, (v: string) => html`<li>${v}</li>`)}</ul>`;
  }
}

async function *tossCoins(count) {
  for (let i=0; i<count; i++) {
    yield Math.random() > 0.5 ? '正面' : '反面';
    await new Promise((r) => setTimeout(r, 1000));
  }
}

class MyElement extends LitElement {
  static properties = {
    tosses: {state: true},
  };

  constructor() {
    super();
    this.tosses = tossCoins(10);
  }

  render() {
    return html`
      <ul>${asyncAppend(this.tosses, (v) => html`<li>${v}</li>`)}</ul>`;
  }
}
customElements.define('my-element', MyElement);

async function *countDown(count: number) {
  while (count > 0) {
    yield count--;
    await new Promise((r) => setTimeout(r, 1000));
  }
}

@customElement('my-element')
class MyElement extends LitElement {

  @state()
  private timer = countDown(10);

  render() {
    return html`计时器：<span>${asyncReplace(this.timer)}</span>.`;
  }
}

async function *countDown(count) {
  while (count > 0) {
    yield count--;
    await new Promise((r) => setTimeout(r, 1000));
  }
}

class MyElement extends LitElement {
  static properties = {
    timer: {state: true},
  };

  constructor() {
    super();
    this.timer = countDown(10);
  }

  render() {
    return html`计时器：<span>${asyncReplace(this.timer)}</span>.`;
  }
}
customElements.define('my-element', MyElement);