pluck.ts
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import { Observable } from '../Observable';
import { map } from './map';
import { OperatorFunction } from '../types';
/* tslint:disable:max-line-length */
export function pluck<T, K1 extends keyof T>(k1: K1): OperatorFunction<T, T[K1]>;
export function pluck<T, K1 extends keyof T, K2 extends keyof T[K1]>(k1: K1, k2: K2): OperatorFunction<T, T[K1][K2]>;
export function pluck<T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2]>(k1: K1, k2: K2, k3: K3): OperatorFunction<T, T[K1][K2][K3]>;
export function pluck<T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2], K4 extends keyof T[K1][K2][K3]>(k1: K1, k2: K2, k3: K3, k4: K4): OperatorFunction<T, T[K1][K2][K3][K4]>;
export function pluck<T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2], K4 extends keyof T[K1][K2][K3], K5 extends keyof T[K1][K2][K3][K4]>(k1: K1, k2: K2, k3: K3, k4: K4, k5: K5): OperatorFunction<T, T[K1][K2][K3][K4][K5]>;
export function pluck<T, K1 extends keyof T, K2 extends keyof T[K1], K3 extends keyof T[K1][K2], K4 extends keyof T[K1][K2][K3], K5 extends keyof T[K1][K2][K3][K4], K6 extends keyof T[K1][K2][K3][K4][K5]>(k1: K1, k2: K2, k3: K3, k4: K4, k5: K5, k6: K6): OperatorFunction<T, T[K1][K2][K3][K4][K5][K6]>;
export function pluck<T, R>(...properties: string[]): OperatorFunction<T, R>;
/* tslint:enable:max-line-length */
/**
* Maps each source value (an object) to its specified nested property.
*
* <span class="informal">Like {@link map}, but meant only for picking one of
* the nested properties of every emitted object.</span>
*
* 
*
* Given a list of strings describing a path to an object property, retrieves
* the value of a specified nested property from all values in the source
* Observable. If a property can't be resolved, it will return `undefined` for
* that value.
*
* ## Example
* Map every click to the tagName of the clicked target element
* ```ts
* import { fromEvent } from 'rxjs';
* import { pluck } from 'rxjs/operators';
*
* const clicks = fromEvent(document, 'click');
* const tagNames = clicks.pipe(pluck('target', 'tagName'));
* tagNames.subscribe(x => console.log(x));
* ```
*
* @see {@link map}
*
* @param {...string} properties The nested properties to pluck from each source
* value (an object).
* @return {Observable} A new Observable of property values from the source values.
* @method pluck
* @owner Observable
*/
export function pluck<T, R>(...properties: string[]): OperatorFunction<T, R> {
const length = properties.length;
if (length === 0) {
throw new Error('list of properties cannot be empty.');
}
return (source: Observable<T>) => map(plucker(properties, length))(source as any);
}
function plucker(props: string[], length: number): (x: string) => any {
const mapper = (x: string) => {
let currentProp = x;
for (let i = 0; i < length; i++) {
const p = currentProp != null ? currentProp[props[i]] : undefined;
if (p !== void 0) {
currentProp = p;
} else {
return undefined;
}
}
return currentProp;
};
return mapper;
}