72 lines
2.4 KiB
TypeScript
72 lines
2.4 KiB
TypeScript
/**
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* @license
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* Copyright Google Inc. All Rights Reserved.
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*
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* Use of this source code is governed by an MIT-style license that can be
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* found in the LICENSE file at https://angular.io/license
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*/
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import {Pipe, PipeTransform} from '@angular/core';
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import {isBlank} from '../facade/lang';
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import {InvalidPipeArgumentError} from './invalid_pipe_argument_error';
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/**
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* @ngModule CommonModule
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* @whatItDoes Creates a new List or String containing a subset (slice) of the elements.
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* @howToUse `array_or_string_expression | slice:start[:end]`
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* @description
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*
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* Where the input expression is a `List` or `String`, and:
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* - `start`: The starting index of the subset to return.
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* - **a positive integer**: return the item at `start` index and all items after
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* in the list or string expression.
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* - **a negative integer**: return the item at `start` index from the end and all items after
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* in the list or string expression.
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* - **if positive and greater than the size of the expression**: return an empty list or string.
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* - **if negative and greater than the size of the expression**: return entire list or string.
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* - `end`: The ending index of the subset to return.
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* - **omitted**: return all items until the end.
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* - **if positive**: return all items before `end` index of the list or string.
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* - **if negative**: return all items before `end` index from the end of the list or string.
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*
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* All behavior is based on the expected behavior of the JavaScript API `Array.prototype.slice()`
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* and `String.prototype.slice()`.
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*
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* When operating on a [List], the returned list is always a copy even when all
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* the elements are being returned.
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*
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* When operating on a blank value, the pipe returns the blank value.
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*
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* ## List Example
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*
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* This `ngFor` example:
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*
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* {@example common/pipes/ts/slice_pipe.ts region='SlicePipe_list'}
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*
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* produces the following:
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*
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* <li>b</li>
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* <li>c</li>
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*
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* ## String Examples
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*
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* {@example common/pipes/ts/slice_pipe.ts region='SlicePipe_string'}
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*
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* @stable
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*/
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@Pipe({name: 'slice', pure: false})
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export class SlicePipe implements PipeTransform {
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transform(value: any, start: number, end?: number): any {
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if (isBlank(value)) return value;
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if (!this.supports(value)) {
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throw new InvalidPipeArgumentError(SlicePipe, value);
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}
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return value.slice(start, end);
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}
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private supports(obj: any): boolean { return typeof obj === 'string' || Array.isArray(obj); }
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}
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