51 lines
1.7 KiB
JavaScript
51 lines
1.7 KiB
JavaScript
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import { map } from './map';
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/**
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* Maps each source value (an object) to its specified nested property.
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*
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* <span class="informal">Like {@link map}, but meant only for picking one of
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* the nested properties of every emitted object.</span>
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*
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* <img src="./img/pluck.png" width="100%">
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*
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* Given a list of strings describing a path to an object property, retrieves
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* the value of a specified nested property from all values in the source
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* Observable. If a property can't be resolved, it will return `undefined` for
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* that value.
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*
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* @example <caption>Map every click to the tagName of the clicked target element</caption>
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* var clicks = Rx.Observable.fromEvent(document, 'click');
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* var tagNames = clicks.pluck('target', 'tagName');
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* tagNames.subscribe(x => console.log(x));
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*
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* @see {@link map}
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*
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* @param {...string} properties The nested properties to pluck from each source
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* value (an object).
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* @return {Observable} A new Observable of property values from the source values.
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* @method pluck
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* @owner Observable
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*/
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export function pluck(...properties) {
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const length = properties.length;
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if (length === 0) {
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throw new Error('list of properties cannot be empty.');
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}
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return (source) => map(plucker(properties, length))(source);
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}
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function plucker(props, length) {
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const mapper = (x) => {
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let currentProp = x;
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for (let i = 0; i < length; i++) {
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const p = currentProp[props[i]];
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if (typeof p !== 'undefined') {
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currentProp = p;
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}
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else {
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return undefined;
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}
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}
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return currentProp;
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};
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return mapper;
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}
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//# sourceMappingURL=pluck.js.map
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