48 lines
1.2 KiB
TypeScript
48 lines
1.2 KiB
TypeScript
// TypeScript port of koa-compose (https://github.com/koajs/compose)
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export type NextFunction = () => Promise<any>;
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export type Middleware<T = any> = (context: T, next: NextFunction) => Promise<any>;
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export function compose<T = any> (middleware: Middleware<T>[]) {
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if (!Array.isArray(middleware)) {
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throw new TypeError('Middleware stack must be an array!');
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}
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for (const fn of middleware) {
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if (typeof fn !== 'function') {
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throw new TypeError('Middleware must be composed of functions!');
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}
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}
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return function (this: any, context: T, next?: Middleware<T>) {
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// last called middleware #
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let index: number = -1;
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return dispatch.call(this, 0);
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function dispatch (this: any, i: number): Promise<any> {
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if (i <= index) {
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return Promise.reject(new Error('next() called multiple times'));
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}
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index = i;
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let fn: Middleware|undefined = middleware[i];
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if (i === middleware.length) {
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fn = next;
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}
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if (!fn) {
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return Promise.resolve();
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}
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try {
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return Promise.resolve(fn.call(this, context, dispatch.bind(this, i + 1)));
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} catch (err) {
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return Promise.reject(err);
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}
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}
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};
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}
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