53 lines
2.3 KiB
JavaScript
53 lines
2.3 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 { directive, PartType, } from '../directive.js';
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import { AsyncReplaceDirective } from './async-replace.js';
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import { clearPart, insertPart, setChildPartValue, } from '../directive-helpers.js';
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class AsyncAppendDirective extends AsyncReplaceDirective {
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// Override AsyncReplace to narrow the allowed part type to ChildPart only
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constructor(partInfo) {
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super(partInfo);
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if (partInfo.type !== PartType.CHILD) {
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throw new Error('asyncAppend can only be used in child expressions');
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}
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}
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// Override AsyncReplace to save the part since we need to append into it
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update(part, params) {
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this.__childPart = part;
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return super.update(part, params);
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}
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// Override AsyncReplace to append rather than replace
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commitValue(value, index) {
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// When we get the first value, clear the part. This lets the
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// previous value display until we can replace it.
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if (index === 0) {
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clearPart(this.__childPart);
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}
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// Create and insert a new part and set its value to the next value
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const newPart = insertPart(this.__childPart);
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setChildPartValue(newPart, value);
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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], appending new
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* values after previous values, similar to the built-in support for iterables.
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* This directive is usable only in child expressions.
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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 appended 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 asyncAppend = directive(AsyncAppendDirective);
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//# sourceMappingURL=async-append.js.map
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