limit.js•1.51 kB
"use strict";
var ensureNaturalNumber = require("type/natural-number/ensure")
, ensurePlainFunction = require("type/plain-function/ensure")
, ensure = require("type/ensure")
, defineFunctionLength = require("../lib/private/define-function-length");
module.exports = function (limit, callback) {
limit = ensure(
["limit", limit, ensureNaturalNumber, { min: 1 }],
["callback", callback, ensurePlainFunction]
)[0];
var Promise = this, ongoingCount = 0, pending = [];
var onSuccess, onFailure;
var release = function () {
--ongoingCount;
if (ongoingCount >= limit) return;
var next = pending.shift();
if (!next) return;
++ongoingCount;
try {
next.resolve(
Promise.resolve(callback.apply(next.context, next.arguments)).then(
onSuccess, onFailure
)
);
} catch (exception) {
release();
next.reject(exception);
}
};
onSuccess = function (value) {
release();
return value;
};
onFailure = function (exception) {
release();
throw exception;
};
return defineFunctionLength(callback.length, function () {
if (ongoingCount >= limit) {
var context = this, args = arguments;
return new Promise(function (resolve, reject) {
pending.push({
context: context,
arguments: args,
resolve: resolve,
reject: reject
});
});
}
++ongoingCount;
try {
return Promise.resolve(callback.apply(this, arguments)).then(onSuccess, onFailure);
} catch (exception) { return onFailure(exception); }
});
};