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slice_pipe.ts
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slice_pipe.ts
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/**
* @license
* Copyright Google LLC All Rights Reserved.
*
* Use of this source code is governed by an MIT-style license that can be
* found in the LICENSE file at https://angular.io/license
*/
import {Pipe, PipeTransform} from '@angular/core';
import {invalidPipeArgumentError} from './invalid_pipe_argument_error';
/**
* @ngModule CommonModule
* @description
*
* Creates a new `Array` or `String` containing a subset (slice) of the elements.
*
* @usageNotes
*
* All behavior is based on the expected behavior of the JavaScript API `Array.prototype.slice()`
* and `String.prototype.slice()`.
*
* When operating on an `Array`, the returned `Array` is always a copy even when all
* the elements are being returned.
*
* When operating on a blank value, the pipe returns the blank value.
*
* ### List Example
*
* This `ngFor` example:
*
* {@example common/pipes/ts/slice_pipe.ts region='SlicePipe_list'}
*
* produces the following:
*
* ```html
* <li>b</li>
* <li>c</li>
* ```
*
* ### String Examples
*
* {@example common/pipes/ts/slice_pipe.ts region='SlicePipe_string'}
*
* @publicApi
*/
@Pipe({
name: 'slice',
pure: false,
standalone: true,
})
export class SlicePipe implements PipeTransform {
/**
* @param value a list or a string to be sliced.
* @param start the starting index of the subset to return:
* - **a positive integer**: return the item at `start` index and all items after
* in the list or string expression.
* - **a negative integer**: return the item at `start` index from the end and all items after
* in the list or string expression.
* - **if positive and greater than the size of the expression**: return an empty list or
* string.
* - **if negative and greater than the size of the expression**: return entire list or string.
* @param end the ending index of the subset to return:
* - **omitted**: return all items until the end.
* - **if positive**: return all items before `end` index of the list or string.
* - **if negative**: return all items before `end` index from the end of the list or string.
*/
transform<T>(value: ReadonlyArray<T>, start: number, end?: number): Array<T>;
transform(value: null|undefined, start: number, end?: number): null;
transform<T>(value: ReadonlyArray<T>|null|undefined, start: number, end?: number): Array<T>|null;
transform(value: string, start: number, end?: number): string;
transform(value: string|null|undefined, start: number, end?: number): string|null;
transform<T>(value: ReadonlyArray<T>|string|null|undefined, start: number, end?: number):
Array<T>|string|null {
if (value == null) return null;
if (!this.supports(value)) {
throw invalidPipeArgumentError(SlicePipe, value);
}
return value.slice(start, end);
}
private supports(obj: any): boolean {
return typeof obj === 'string' || Array.isArray(obj);
}
}