koa-lite/lib/compose.js

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/**
* Lifted from koa-compose package.
*/
'use strict';
/**
* Compose `middleware` returning
* a fully valid middleware comprised
* of all those which are passed.
*
* @param {Array} middleware
* @return {Function}
* @api public
*/
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, dispatch.bind(null, i + 1)));
} catch (err) {
return Promise.reject(err);
}
}
};
}
/**
* Expose compositor.
*/
module.exports = compose;