100 lines
4.2 KiB
JavaScript
100 lines
4.2 KiB
JavaScript
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/**
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* @license
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* Copyright 2017 Google LLC
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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import { noChange } from '../lit-html.js';
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import { AsyncDirective, directive, } from '../async-directive.js';
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import { Pauser, PseudoWeakRef, forAwaitOf } from './private-async-helpers.js';
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export class AsyncReplaceDirective extends AsyncDirective {
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constructor() {
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super(...arguments);
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this.__weakThis = new PseudoWeakRef(this);
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this.__pauser = new Pauser();
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}
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// @ts-expect-error value not used, but we want a nice parameter for docs
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// eslint-disable-next-line @typescript-eslint/no-unused-vars
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render(value, _mapper) {
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return noChange;
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}
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update(_part, [value, mapper]) {
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// If our initial render occurs while disconnected, ensure that the pauser
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// and weakThis are in the disconnected state
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if (!this.isConnected) {
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this.disconnected();
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}
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// If we've already set up this particular iterable, we don't need
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// to do anything.
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if (value === this.__value) {
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return noChange;
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}
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this.__value = value;
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let i = 0;
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const { __weakThis: weakThis, __pauser: pauser } = this;
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// Note, the callback avoids closing over `this` so that the directive
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// can be gc'ed before the promise resolves; instead `this` is retrieved
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// from `weakThis`, which can break the hard reference in the closure when
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// the directive disconnects
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forAwaitOf(value, async (v) => {
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// The while loop here handles the case that the connection state
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// thrashes, causing the pauser to resume and then get re-paused
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while (pauser.get()) {
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await pauser.get();
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}
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// If the callback gets here and there is no `this`, it means that the
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// directive has been disconnected and garbage collected and we don't
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// need to do anything else
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const _this = weakThis.deref();
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if (_this !== undefined) {
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// Check to make sure that value is the still the current value of
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// the part, and if not bail because a new value owns this part
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if (_this.__value !== value) {
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return false;
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}
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// As a convenience, because functional-programming-style
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// transforms of iterables and async iterables requires a library,
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// we accept a mapper function. This is especially convenient for
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// rendering a template for each item.
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if (mapper !== undefined) {
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v = mapper(v, i);
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}
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_this.commitValue(v, i);
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i++;
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}
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return true;
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});
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return noChange;
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}
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// Override point for AsyncAppend to append rather than replace
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commitValue(value, _index) {
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this.setValue(value);
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}
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disconnected() {
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this.__weakThis.disconnect();
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this.__pauser.pause();
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}
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reconnected() {
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this.__weakThis.reconnect(this);
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this.__pauser.resume();
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}
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}
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/**
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* A directive that renders the items of an async iterable[1], replacing
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* previous values with new values, so that only one value is ever rendered
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* at a time. This directive may be used in any expression type.
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*
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* Async iterables are objects with a `[Symbol.asyncIterator]` method, which
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* returns an iterator who's `next()` method returns a Promise. When a new
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* value is available, the Promise resolves and the value is rendered to the
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* Part controlled by the directive. If another value other than this
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* directive has been set on the Part, the iterable will no longer be listened
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* to and new values won't be written to the Part.
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*
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* [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for-await...of
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*
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* @param value An async iterable
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* @param mapper An optional function that maps from (value, index) to another
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* value. Useful for generating templates for each item in the iterable.
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*/
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export const asyncReplace = directive(AsyncReplaceDirective);
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//# sourceMappingURL=async-replace.js.map
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