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

77 lines
2.9 KiB
JavaScript

/**
* @license
* Copyright 2020 Google LLC
* SPDX-License-Identifier: BSD-3-Clause
*/
import { noChange, nothing } from '../lit-html.js';
import { directive, Directive, PartType, } from '../directive.js';
import { isSingleExpression, setCommittedValue } from '../directive-helpers.js';
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.
*/
export const live = directive(LiveDirective);
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