sc-fitted-text.html

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<link rel="import" href="../polymer/polymer-element.html">
<link rel="import" href="../polymer/lib/utils/render-status.html">
<link rel="import" href="../polymer/lib/utils/debounce.html">
<link rel="import" href="../shadycss/apply-shim.html">

<!--
A Polymer 2 element for horizontally squishing text to stay within a max width.

### Styling

The following mixins are available for styling:

Mixin | Description | Default
----------------|-------------|----------
`--sc-fitted-text-content` | Mixin applied to the internal text div | `{}`

@demo demo/index.html
-->

<dom-module id="sc-fitted-text">
	<template>
		<style>
			:host {
				display: flex;
				white-space: nowrap;
			}

			#fittedContent {
				visibility: hidden; /* hide until fonts load */
				@apply --sc-fitted-text-content;
			}
		</style>

		<div id="fittedContent"></div>
	</template>

	<script>
		/**
		 * @customElement
		 * @polymer
		 */
		class ScFittedText extends Polymer.Element {
			static get is() {
				return 'sc-fitted-text';
			}

			static get properties() {
				return {
					text: {
						type: String,
						observer: '_textChanged'
					},
					maxWidth: {
						type: Number,
						value: 0,
						observer: '_maxWidthChanged'
					},
					align: {
						type: String,
						value: 'left',
						observer: '_alignChanged'
					}
				};
			}

			/**
			 * Re-fit the text to maxWidth.
			 * It should rarely be necessary to manually call this, as it will be automatically
			 * called whenever the `text` or `maxWidth` properties change.
			 */
			fit() {
				this._fitDebouncer = Polymer.Debouncer.debounce(
					this._fitDebouncer,
					Polymer.Async.timeOut.after(0),
					this._fit.bind(this)
				);
			}

			/**
			 * The public `fit` method is actually a debouncer.
			 * This private method is what does the fitting.
			 * @private
			 */
			_fit() {
				Polymer.RenderStatus.beforeNextRender(this, () => {
					this.$.fittedContent.style.transform = 'scaleX(1)';

					const maxWidth = parseInt(this.maxWidth, 10);
					if (isNaN(maxWidth) || maxWidth <= 0) {
						return;
					}

					const scrollWidth = this.$.fittedContent.scrollWidth;
					if (scrollWidth > maxWidth) {
						this.$.fittedContent.style.transform = `scaleX(${maxWidth / scrollWidth})`;
					} else {
						this.$.fittedContent.style.transform = 'scaleX(1)';
					}
				});
			}

			/**
			 * When the `text` property changes.
			 * @param {String} newVal
			 * @private
			 */
			_textChanged(newVal) {
				this.$.fittedContent.textContent = newVal;

				if (document.readyState !== 'complete') {
					window.addEventListener('load', () => {
						this._textChanged(this.text);
					});
					return;
				}

				const font = window.getComputedStyle(this.$.fittedContent).font;
				if (!font) {
					this.$.fittedContent.style.visibility = 'visible';
					this.fit();
					return;
				}

				document.fonts.load(font).then(() => {
					this.$.fittedContent.style.visibility = 'visible';
					this.fit();
				}).catch(e => {
					console.error('Failed to load fonts:', e);
				});
			}

			/**
			 * When the `maxWidth` property changes.
			 * @param {String} newVal
			 * @private
			 */
			_maxWidthChanged(newVal) {
				this.style.maxWidth = newVal <= 0 ? '' : `${newVal}px`;
				this.fit();
			}

			/**
			 * When the `align` property changes.
			 * @param {String} newVal
			 * @private
			 */
			_alignChanged(newVal) {
				switch (newVal) {
					case 'center':
						this.style.justifyContent = 'center';
						this.$.fittedContent.style.transformOrigin = 'center';
						this.$.fittedContent.style.textAlign = 'center';
						break;
					case 'left':
						this.style.justifyContent = '';
						this.$.fittedContent.style.transformOrigin = 'left';
						this.$.fittedContent.style.textAlign = 'left';
						break;
					case 'right':
						this.style.justifyContent = 'flex-end';
						this.$.fittedContent.style.transformOrigin = 'right';
						this.$.fittedContent.style.textAlign = 'right';
						break;
					default:
						throw new Error(`Unexpected align value: ${newVal}`);
				}
			}
		}

		customElements.define(ScFittedText.is, ScFittedText);
	</script>
</dom-module>