58 lines
1.9 KiB
JavaScript
58 lines
1.9 KiB
JavaScript
//#region src/compat/function/bindKey.ts
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/**
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* Creates a function that invokes the method at `object[key]` with `partialArgs` prepended to the arguments it receives.
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*
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* This method differs from `bind` by allowing bound functions to reference methods that may be redefined or don't yet exist.
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*
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* The `bindKey.placeholder` value, which defaults to a `symbol`, may be used as a placeholder for partially applied arguments.
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*
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* @template T - The type of the object to bind.
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* @template K - The type of the key to bind.
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* @param {T} object - The object to invoke the method on.
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* @param {K} key - The key of the method.
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* @param {...any} partialArgs - The arguments to be partially applied.
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* @returns {T[K] extends (...args: any[]) => any ? (...args: any[]) => ReturnType<T[K]> : never} - Returns the new bound function.
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*
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* @example
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* const object = {
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* user: 'fred',
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* greet: function (greeting, punctuation) {
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* return greeting + ' ' + this.user + punctuation;
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* },
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* };
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*
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* let bound = bindKey(object, 'greet', 'hi');
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* bound('!');
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* // => 'hi fred!'
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*
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* object.greet = function (greeting, punctuation) {
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* return greeting + 'ya ' + this.user + punctuation;
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* };
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*
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* bound('!');
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* // => 'hiya fred!'
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*
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* // Bound with placeholders.
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* bound = bindKey(object, 'greet', bindKey.placeholder, '!');
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* bound('hi');
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* // => 'hiya fred!'
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*/
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function bindKey(object, key, ...partialArgs) {
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const bound = function(...providedArgs) {
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const args = [];
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let startIndex = 0;
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for (let i = 0; i < partialArgs.length; i++) {
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const arg = partialArgs[i];
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if (arg === bindKey.placeholder) args.push(providedArgs[startIndex++]);
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else args.push(arg);
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}
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for (let i = startIndex; i < providedArgs.length; i++) args.push(providedArgs[i]);
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if (this instanceof bound) return new object[key](...args);
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return object[key].apply(object, args);
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};
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return bound;
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}
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bindKey.placeholder = Symbol("bindKey.placeholder");
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//#endregion
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exports.bindKey = bindKey;
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