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'use strict';
import identity from 'lodash/identity';
import rest from 'lodash/rest';
import setImmediate from './internal/setImmediate';
import initialParams from './internal/initialParams';
function has(obj, key) {
return key in obj;
}
/**
* Caches the results of an `async` function. When creating a hash to store
* function results against, the callback is omitted from the hash and an
* optional hash function can be used.
*
* If no hash function is specified, the first argument is used as a hash key,
* which may work reasonably if it is a string or a data type that converts to a
* distinct string. Note that objects and arrays will not behave reasonably.
* Neither will cases where the other arguments are significant. In such cases,
* specify your own hash function.
*
* The cache of results is exposed as the `memo` property of the function
* returned by `memoize`.
*
* @name memoize
* @static
* @memberOf async
* @category Util
* @param {Function} fn - The function to proxy and cache results from.
* @param {Function} hasher - An optional function for generating a custom hash
* for storing results. It has all the arguments applied to it apart from the
* callback, and must be synchronous.
* @example
*
* var slow_fn = function(name, callback) {
* // do something
* callback(null, result);
* };
* var fn = async.memoize(slow_fn);
*
* // fn can now be used as if it were slow_fn
* fn('some name', function() {
* // callback
* });
*/
export default function memoize(fn, hasher) {
var memo = Object.create(null);
var queues = Object.create(null);
hasher = hasher || identity;
var memoized = initialParams(function memoized(args, callback) {
var key = hasher.apply(null, args);
if (has(memo, key)) {
setImmediate(function() {
callback.apply(null, memo[key]);
});
} else if (has(queues, key)) {
queues[key].push(callback);
} else {
queues[key] = [callback];
fn.apply(null, args.concat([rest(function(args) {
memo[key] = args;
var q = queues[key];
delete queues[key];
for (var i = 0, l = q.length; i < l; i++) {
q[i].apply(null, args);
}
})]));
}
});
memoized.memo = memo;
memoized.unmemoized = fn;
return memoized;
}
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