e520319af2
The intention of the code is (1) to return target if none of the setters lead to an actual change, (2) to not modify target, and (3) to do it with a 1 copyOnWrite at most.
139 lines
4.8 KiB
JavaScript
139 lines
4.8 KiB
JavaScript
/* @flow */
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import _ from 'lodash';
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/**
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* Sets specific properties of a specific state to specific values and prevents
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* unnecessary state changes.
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*
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* @param {Object} target - The state on which the specified properties are to
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* be set.
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* @param {Object} source - The map of properties to values which are to be set
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* on the specified target.
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* @returns {Object} The specified target if the values of the specified
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* properties equal the specified values; otherwise, a new state constructed
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* from the specified target by setting the specified properties to the
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* specified values.
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*/
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export function assign(target: Object, source: Object) {
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let t = target;
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for (const property in source) { // eslint-disable-line guard-for-in
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t = _set(t, property, source[property], t === target);
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}
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return t;
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}
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/**
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* Determines whether {@code a} equals {@code b} according to deep comparison
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* (which makes sense for Redux and its state definition).
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*
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* @param {*} a - The value to compare to {@code b}.
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* @param {*} b - The value to compare to {@code a}.
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* @returns {boolean} True if {@code a} equals {@code b} (according to deep
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* comparison); false, otherwise.
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*/
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export function equals(a: any, b: any) {
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return _.isEqual(a, b);
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}
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/**
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* Sets a specific property of a specific state to a specific value. Prevents
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* unnecessary state changes (when the specified {@code value} is equal to the
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* value of the specified {@code property} of the specified {@code state}).
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*
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* @param {Object} state - The (Redux) state from which a new state is to be
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* constructed by setting the specified {@code property} to the specified
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* {@code value}.
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* @param {string} property - The property of {@code state} which is to be
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* assigned the specified {@code value} (in the new state).
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* @param {*} value - The value to assign to the specified {@code property}.
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* @returns {Object} The specified {@code state} if the value of the specified
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* {@code property} equals the specified <tt>value/tt>; otherwise, a new state
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* constructed from the specified {@code state} by setting the specified
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* {@code property} to the specified {@code value}.
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*/
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export function set(state: Object, property: string, value: any) {
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return _set(state, property, value, /* copyOnWrite */ true);
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}
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/* eslint-disable max-params */
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/**
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* Sets a specific property of a specific state to a specific value. Prevents
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* unnecessary state changes (when the specified {@code value} is equal to the
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* value of the specified {@code property} of the specified {@code state}).
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*
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* @param {Object} state - The (Redux) state from which a state is to be
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* constructed by setting the specified {@code property} to the specified
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* {@code value}.
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* @param {string} property - The property of {@code state} which is to be
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* assigned the specified {@code value}.
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* @param {*} value - The value to assign to the specified {@code property}.
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* @param {boolean} copyOnWrite - If the specified {@code state} is to not be
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* modified, {@code true}; otherwise, {@code false}.
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* @returns {Object} The specified {@code state} if the value of the specified
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* {@code property} equals the specified <tt>value/tt> or {@code copyOnWrite}
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* is truthy; otherwise, a new state constructed from the specified
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* {@code state} by setting the specified {@code property} to the specified
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* {@code value}.
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*/
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function _set(
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state: Object,
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property: string,
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value: any,
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copyOnWrite: boolean) {
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// Delete state properties that are to be set to undefined. (It is a matter
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// of personal preference, mostly.)
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if (typeof value === 'undefined'
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&& Object.prototype.hasOwnProperty.call(state, property)) {
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const newState = copyOnWrite ? { ...state } : state;
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if (delete newState[property]) {
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return newState;
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}
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}
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if (state[property] !== value) {
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if (copyOnWrite) {
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return {
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...state,
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[property]: value
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};
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}
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state[property] = value;
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}
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return state;
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}
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/* eslint-enable max-params */
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/**
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* Returns redux state from the specified {@code stateful} which is presumed to
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* be related to the redux state (e.g. the redux store, the redux
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* {@code getState} function).
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*
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* @param {Function|Object} stateful - The entity such as the redux store or the
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* redux {@code getState} function from which the redux state is to be
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* returned.
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* @returns {Object} The redux state.
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*/
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export function toState(stateful: Function | Object) {
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if (stateful) {
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if (typeof stateful === 'function') {
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return stateful();
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}
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const { getState } = stateful;
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if (typeof getState === 'function') {
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return getState();
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}
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}
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return stateful;
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}
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