60 lines
1.8 KiB
TypeScript
60 lines
1.8 KiB
TypeScript
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/**
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* @license
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* Copyright 2018 Google LLC
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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import { Part } from '../lit-html.js';
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import { Directive, DirectiveParameters } from '../directive.js';
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declare class GuardDirective extends Directive {
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private _previousValue;
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render(_value: unknown, f: () => unknown): unknown;
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update(_part: Part, [value, f]: DirectiveParameters<this>): unknown;
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}
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/**
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* Prevents re-render of a template function until a single value or an array of
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* values changes.
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*
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* Values are checked against previous values with strict equality (`===`), and
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* so the check won't detect nested property changes inside objects or arrays.
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* Arrays values have each item checked against the previous value at the same
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* index with strict equality. Nested arrays are also checked only by strict
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* equality.
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*
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* Example:
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*
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* ```js
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* html`
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* <div>
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* ${guard([user.id, company.id], () => html`...`)}
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* </div>
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* `
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* ```
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*
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* In this case, the template only rerenders if either `user.id` or `company.id`
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* changes.
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*
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* guard() is useful with immutable data patterns, by preventing expensive work
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* until data updates.
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*
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* Example:
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*
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* ```js
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* html`
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* <div>
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* ${guard([immutableItems], () => immutableItems.map(i => html`${i}`))}
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* </div>
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* `
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* ```
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*
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* In this case, items are mapped over only when the array reference changes.
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*
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* @param value the value to check before re-rendering
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* @param f the template function
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*/
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export declare const guard: (_value: unknown, f: () => unknown) => import("../directive.js").DirectiveResult<typeof GuardDirective>;
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/**
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* The type of the class that powers this directive. Necessary for naming the
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* directive's return type.
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*/
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export type { GuardDirective };
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//# sourceMappingURL=guard.d.ts.map
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