node_modules/lit-html/node/development/directives/live.js

import { noChange, nothing } from '../lit-html.js';
import { directive, Directive, PartType } from '../directive.js';
import { isSingleExpression, setCommittedValue } from '../directive-helpers.js';

/**
 * @license
 * Copyright 2020 Google LLC
 * SPDX-License-Identifier: BSD-3-Clause
 */
class LiveDirective extends Directive {
    constructor(partInfo) {
        super(partInfo);
        if (!(partInfo.type === PartType.PROPERTY ||
            partInfo.type === PartType.ATTRIBUTE ||
            partInfo.type === PartType.BOOLEAN_ATTRIBUTE)) {
            throw new Error('The `live` directive is not allowed on child or event bindings');
        }
        if (!isSingleExpression(partInfo)) {
            throw new Error('`live` bindings can only contain a single expression');
        }
    }
    render(value) {
        return value;
    }
    update(part, [value]) {
        if (value === noChange || value === nothing) {
            return value;
        }
        const element = part.element;
        const name = part.name;
        if (part.type === PartType.PROPERTY) {
            // eslint-disable-next-line @typescript-eslint/no-explicit-any
            if (value === element[name]) {
                return noChange;
            }
        }
        else if (part.type === PartType.BOOLEAN_ATTRIBUTE) {
            if (!!value === element.hasAttribute(name)) {
                return noChange;
            }
        }
        else if (part.type === PartType.ATTRIBUTE) {
            if (element.getAttribute(name) === String(value)) {
                return noChange;
            }
        }
        // Resets the part's value, causing its dirty-check to fail so that it
        // always sets the value.
        setCommittedValue(part);
        return value;
    }
}
/**
 * Checks binding values against live DOM values, instead of previously bound
 * values, when determining whether to update the value.
 *
 * This is useful for cases where the DOM value may change from outside of
 * lit-html, such as with a binding to an `<input>` element's `value` property,
 * a content editable elements text, or to a custom element that changes it's
 * own properties or attributes.
 *
 * In these cases if the DOM value changes, but the value set through lit-html
 * bindings hasn't, lit-html won't know to update the DOM value and will leave
 * it alone. If this is not what you want--if you want to overwrite the DOM
 * value with the bound value no matter what--use the `live()` directive:
 *
 * ```js
 * html`<input .value=${live(x)}>`
 * ```
 *
 * `live()` performs a strict equality check against the live DOM value, and if
 * the new value is equal to the live value, does nothing. This means that
 * `live()` should not be used when the binding will cause a type conversion. If
 * you use `live()` with an attribute binding, make sure that only strings are
 * passed in, or the binding will update every render.
 */
const live = directive(LiveDirective);

export { live };
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