68 lines
1.9 KiB
TypeScript
68 lines
1.9 KiB
TypeScript
/**
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* @author Martin Karkowski
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* @email m.karkowski@zema.de
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* @create date 2020-08-25 23:01:24
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* @modify date 2020-11-07 00:35:49
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* @desc [description]
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*/
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/**
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* Function to get a singleton. To create the singleton, the parameter *create* is used. This will be called once.
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* The singleton will be stored as *global* variable and can be accessed by the identifier
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*
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* @author M.Karkowski
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* @export
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* @template T The Type of the singleton
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* @param {string} identifier Identifier to access the singleton
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* @param {() => T} create The Callback which is used to create the instance.
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* @return An object, containing the key **instances**, where you'll find the instance and an helper function **setInstance** to redefine the instance
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*/
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export function getSingleton<T>(
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identifier: string,
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create: () => T
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): {
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instance: T;
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setInstance: (value: T) => void;
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} {
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// Extract all
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const globalSymbols = Object.getOwnPropertySymbols(global);
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// create a unique, global symbol name
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// -----------------------------------
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const IDENTIFIER_DISPATCHER_CONTAINER = Symbol.for(identifier);
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// check if the global object has this symbol
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// add it if it does not have the symbol, yet
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// ------------------------------------------
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const hasContainer =
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globalSymbols.indexOf(IDENTIFIER_DISPATCHER_CONTAINER) > -1;
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if (!hasContainer) {
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global[IDENTIFIER_DISPATCHER_CONTAINER] = create();
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}
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const ret: {
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instance: T;
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setInstance: (value: T) => void;
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} = {
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instance: global[IDENTIFIER_DISPATCHER_CONTAINER],
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setInstance: (value: T) => {
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global[IDENTIFIER_DISPATCHER_CONTAINER] = value;
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},
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};
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// define the singleton API
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// ------------------------
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Object.defineProperty(ret, "instance", {
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get: function () {
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return global[IDENTIFIER_DISPATCHER_CONTAINER];
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},
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});
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// ensure the API is never changed
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// -------------------------------
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Object.freeze(ret);
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return ret;
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}
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