[article] Create a lit cheat sheet

packages/lit-dev-content/samples/articles/lit-cheat-sheet/add-styles/index.html

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+<script type="module" src="./my-element.js"></script>
+
+<my-element></my-element>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/add-styles/my-element.ts

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+import { html, LitElement, css } from 'lit';
+import { customElement } from 'lit/decorators.js';
+
+@customElement('my-element')
+export class MyElement extends LitElement {
+  render() {
+    return html`<p>I'm blue</p><div>I'm red</div>`;
+  }
+
+  static styles = css`
+    p {
+      color: blue;
+    }
+    div {
+      color: red;
+    }
+  `;
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/add-styles/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "my-element.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "100px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/classes/index.html

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+<script type="module" src="./my-element.js"></script>
+
+<my-element></my-element>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/classes/my-element.ts

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+import { html, LitElement, css } from 'lit';
+import { customElement, state } from 'lit/decorators.js';
+import { classMap } from 'lit/directives/class-map.js';
+
+@customElement('my-element')
+export class MyElement extends LitElement {
+  @state() counter = 0
+
+  firstUpdated() {
+    setInterval(() =>  this.counter += 1 , 1000);
+  }
+
+  render() {
+    const classes = {
+      red: this.counter % 2 === 0,
+      blue: this.counter % 2 === 1
+    };
+    return html`<p class=${classMap(classes)}>Hello!</p>`;
+  }
+
+  static styles = css`
+    .red {
+      color: red;
+    }
+    .blue {
+      color: blue;
+    }
+  `;
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/classes/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "my-element.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "100px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/conditionals/index.html

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+<script type="module" src="./my-element.js"></script>
+
+<my-element></my-element>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/conditionals/my-element.ts

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+import { html, LitElement } from 'lit';
+import { customElement, state } from 'lit/decorators.js';
+
+@customElement('my-element')
+export class MyElement extends LitElement {
+  @state() private someBoolean = false;
+
+  render() {
+    let someText = html`<p>Some text</p>`;
+
+    if (this.someBoolean) {
+      someText = html`<p>Some other text</p>`;
+    }
+
+    return html`
+      <button
+          @click=${() => {this.someBoolean = !this.someBoolean}}>
+        Toggle template
+      </button>
+      <div>This is an inline ternary conditional</div>
+      ${this.someBoolean ? html`<p>Some other text</p>` : html`<p>Some text</p>`}
+      <div>This is a variable conditional</div>
+      ${someText}
+    `;
+  }
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/conditionals/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "my-element.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "200px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/css-shadow-parts/index.html

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+<script type="module" src="./my-element.js"></script>
+<style>
+  .styled my-element::part(paragraph) {
+    color: yellow;
+    border-color: white;
+    padding: 8px;
+    margin: 2px;
+  }
+
+  .styled {
+    background-color: black;
+  }
+
+  div {
+    padding: 4px;
+  }
+</style>
+
+<div class="styled">
+  <my-element></my-element>
+</div>
+<div>
+  <my-element></my-element>
+</div>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/css-shadow-parts/my-element.ts

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+import { html, LitElement, css } from 'lit';
+import { customElement } from 'lit/decorators.js';
+
+@customElement('my-element')
+export class MyElement extends LitElement {
+  static styles = css`
+    p {
+      color: blue;
+      border: 1px solid black;
+      padding: 4px;
+      margin-block: 4px;
+    }
+  `;
+
+  render() {
+    return html`<p part="paragraph">This is in a shadow root!</p>`;
+  }
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/css-shadow-parts/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "my-element.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "120px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/custom-attribute-converter/index.html

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+<script type="module" src="./my-element.js"></script>
+
+<my-element array='1,"2",3,4,"5"'></my-element>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/custom-attribute-converter/my-element.ts

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+import { html, LitElement } from 'lit';
+import { customElement, property, state } from 'lit/decorators.js';import {ComplexAttributeConverter} from 'lit';
+
+/**
+ * Bidirectionally converts an array from an attribute to a property of the
+ * following format:
+ *
+ * array-attribute='1, "2", 3' to [1, '2', 3]
+ */
+export const arrayConverter: ComplexAttributeConverter<Array<unknown>> = {
+  toAttribute: (array: Array<unknown>) => {
+    return JSON.stringify(array).substring(1, JSON.stringify(array).length - 1);
+  },
+  fromAttribute: (value: string) => {
+    try {
+      return JSON.parse(`[${value}]`);
+    } catch {
+      return [];
+    }
+  }
+};
+
+@customElement('my-element')
+export class MyElement extends LitElement {
+  @property({ converter: arrayConverter, reflect: true })
+  array: Array<number|string> = [];
+
+  render() {
+    return this.array.map((item) =>
+      html`<div>${typeof item}: ${item}</div>`
+    );
+  }
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/custom-attribute-converter/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "my-element.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "200px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/data-up/game-player.ts

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+import { html, LitElement } from 'lit';
+import { customElement } from 'lit/decorators.js';
+
+export type ScoreEvent = CustomEvent<number>;
+
+@customElement('game-player')
+export class GamePlayer extends LitElement {
+  render() {
+    return html`
+      <button @click=${() => this.handleScore(7)}>Touchdown!</button>
+      <button @click=${() => this.handleScore(3)}>Field goal!</button>
+    `;
+  }
+
+  handleScore(points: number) {
+    this.dispatchEvent(new CustomEvent('score', { detail: points, bubbles: true }));
+  }
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/data-up/index.html

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+<script type="module" src="./score-board.js"></script>
+
+<score-board></score-board>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/data-up/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "score-board.ts": {},
+    "game-player.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "250px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/data-up/score-board.ts

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+import { html, LitElement } from 'lit';
+import { customElement, state } from 'lit/decorators.js';
+import './game-player.js';
+import type {ScoreEvent} from './game-player.js';
+
+@customElement('score-board')
+export class ScoreBoard extends LitElement {
+  @state() playerOneScore = 0;
+  @state() playerTwoScore = 0;
+
+  render() {
+    return html`
+      <h1>${this.playerOneScore} - ${this.playerTwoScore}</h1>
+      <h2>Player 1</h2>
+      <game-player @score=${(e: ScoreEvent) => this.playerOneScore += e.detail}></game-player>
+      <h2>Player 2</h2>
+      <game-player @score=${(e: ScoreEvent) => this.playerTwoScore += e.detail}></game-player>
+    `;
+  }
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/define/hello-world.ts

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+import { html, LitElement } from 'lit';
+import { customElement } from 'lit/decorators.js';
+
+@customElement('hello-world')
+export class HelloWorld extends LitElement {
+  render() {
+    return html`<p>Hello, world!</p>`;
+  }
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/define/index.html

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+<script type="module" src="./hello-world.js"></script>
+
+<hello-world></hello-world>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/define/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "hello-world.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "100px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/dom-query/index.html

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+<script type="module" src="./my-element.js"></script>
+
+<my-element></my-element>

packages/lit-dev-content/samples/articles/lit-cheat-sheet/dom-query/my-element.ts

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+import { html, LitElement, css } from 'lit';
+import { customElement, state, query } from 'lit/decorators.js';
+
+@customElement('my-element')
+export class MyElement extends LitElement {
+  @state() private canvasText = 'Hello World!';
+  // You can use any querySelector selector
+  @query('#canvasId') private canvasEl!: HTMLCanvasElement;
+
+  render() {
+    return html`
+      <canvas id="canvasId"></canvas>
+      <label>
+        Enter text to draw in canvas:
+        <input @input=${this.handleInput} .value=${this.canvasText}>
+      </label>
+    `;
+  }
+
+  private setCanvasText(text: string) {
+    this.canvasText = text;
+    // Access the canvas elemtnwith this.canvasEl
+    const ctx = this.canvasEl.getContext("2d");
+
+    if (!ctx) {
+      return;
+    }
+
+    ctx.clearRect(0, 0, this.canvasEl.width, this.canvasEl.height);
+    ctx.font = "50px Arial";
+    ctx.fillText(this.canvasText,10,80);
+  }
+
+  private handleInput(event: Event) {
+    this.setCanvasText((event.target as HTMLInputElement).value);
+  }
+
+  protected firstUpdated() {
+    // DOM is typically ready for the first time by firstUpdated()
+    this.setCanvasText(this.canvasText);
+  }
+
+  static styles = css`
+    canvas {
+      border: 1px solid black;
+    }
+
+    label {
+      display: block;
+      margin-block-start: 1em;
+    }
+  `;
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/dom-query/project.json

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+{
+  "extends": "/samples/v3-base.json",
+  "files": {
+    "my-element.ts": {},
+    "index.html": {}
+  },
+  "previewHeight": "230px"
+}

packages/lit-dev-content/samples/articles/lit-cheat-sheet/event-listeners/index.html

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+<script type="module" src="./my-element.js"></script>
+
+<my-element></my-element>