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nextState.js
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nextState.js
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/**
* @module nextState
* @private
*/
/**
* Creates the next state tree from the current state tree and some updates.
*
* N.B. OO.copy doesn't copy Element instances, whereas $.extend does.
* However, OO.copy does copy properties whose values are undefined or null,
* whereas $.extend doesn't. Since the state tree contains an Element instance
* - the preview.activeLink property - and we want to copy undefined/null into
* the state we need to manually iterate over updates and check with
* hasOwnProperty to copy over to the new state.
*
* In [change listeners](/docs/change_listener.md), for example, we talk about
* the previous state and the current state (the `oldState` and `newState`
* parameters, respectively). Since
* [reducers](http://redux.js.org/docs/basics/Reducers.html) take the current
* state and an action and make updates, "next state" seems appropriate.
*
* @param {Object} state
* @param {Object} updates
* @return {Object}
*/
export default function nextState( state, updates ) {
const hasOwn = Object.prototype.hasOwnProperty,
result = {};
// Flat clone of everything that's not updated
for ( const key in state ) {
if ( hasOwn.call( state, key ) && !hasOwn.call( updates, key ) ) {
result[ key ] = state[ key ];
}
}
for ( const key in updates ) {
if ( !hasOwn.call( updates, key ) ) {
continue;
}
// Deep clone only if there is an update
if ( isObject( updates[ key ] ) ) {
const clone = state[ key ] ? nextState( {}, state[ key ] ) : {};
// Recursion
result[ key ] = nextState( clone, updates[ key ] );
} else {
result[ key ] = updates[ key ];
}
}
return result;
}
/**
* @param {any} obj
* @return {boolean}
*/
function isObject( obj ) {
// https://javascript.plainenglish.io/javascript-check-if-a-variable-is-an-object-and-nothing-else-not-an-array-a-set-etc-a3987ea08fd7
return obj && obj.constructor === Object;
}

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