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function compose (middleware) { | |
if (!Array.isArray(middleware)) throw new TypeError('Middleware stack must be an array!') | |
for (const fn of middleware) { | |
if (typeof fn !== 'function') throw new TypeError('Middleware must be composed of functions!') | |
} | |
/** | |
* @param {Object} context | |
* @return {Promise} | |
* @api public | |
*/ | |
return function (context, next) { | |
// last called middleware # | |
let index = -1 | |
return dispatch(0) | |
function dispatch (i) { | |
if (i <= index) return Promise.reject(new Error('next() called multiple times')) | |
index = i | |
let fn = middleware[i] | |
if (i === middleware.length) fn = next | |
if (!fn) return Promise.resolve() | |
try { | |
return Promise.resolve(fn(context, function next () { | |
return dispatch(i + 1) | |
})) | |
} catch (err) { | |
return Promise.reject(err) | |
} | |
} | |
} | |
} |
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