node-memoizesync

Yet another memoizer for synchronous functions.

var memoizeSync = require('memoizesync');

function myExpensiveComputation(arg1, arg2) {
    // ...
    return result;
}

var memoized = memoizeSync(myExpensiveComputation, options);

Now memoized works exactly like myExpensiveComputation, except that the actual computation is only performed once for each unique set of arguments:

var result = memoized(42, 100);
// Got the result!

var result2 = memoized(42, 100);
// Got the same result, and much faster this time!

The function returned by memoizeSync invokes the wrapped function in the context it's called in itself, so memoizeSync even works for memoizing a method that has access to instance variables:

function Foo(name) {
    this.name = name;

    this.myMethod = memoizeSync(function (arg1, arg2) {
        console.log("Cool, this.name works here!", this.name);
        // ...
        return "That was tough, but I'm done now!";
    });
}

(Unfortunately setting Foo.prototype.myMethod = memoizeSync(...) wouldn't work as the memoizer would be shared among all instances of Foo).

To distinguish different invocations (whose results need to be cached separately) memoizeSync relies on a naive stringification of the arguments, which is looked up in an internally kept hash. If the function you're memoizing takes non-primitive arguments you might want to provide a custom argumentsStringifier in the options argument to memoizeSync. Otherwise all object arguments will be considered equal because they stringify to [object Object]:

var memoized = memoizeSync(function functionToMemoize(obj) {
    // ...
    return Object.keys(obj).join('');
}, {
    argumentsStringifier: function (args) {
        return args.map(function (arg) {return JSON.stringify(arg);}).join(",");
    }
);

memoized({foo: 'bar'}); // 'foo'

memoized({quux: 'baz'}); // 'quux'

Had the custom argumentsStringifier not been provided, the memoized function would would have returned foo both times.

If the argumentsStringifier returns false, the cache will be bypassed.

Check out the custom argumentsStringifier test for another example.

Purging and expiring memoized values

You can forcefully clear a specific memoized value using the purge method on the memoizer:

var memoized = memoizeSync(function functionToMemoize(foo) {
    // ...
    return theResult;
});
var foo = memoized(123);
memoized.purge(123);
foo = memoized(123); // Will be recomputed

memoizer.purgeAll() clears all memoized results.

You can also specify a custom ttl (in milliseconds) on the memoized results:

var memoized = memoizeSync(function functionToMemoize() {
    // ...
    return theResult;
}, {maxAge: 1000});

In the above example the memoized value will be considered stale one second after it has been computed, and it will be recomputed next time memoizeSync is invoked with the same arguments.

memoizeSync uses node-lru-cache to store the memoized values, and it accepts the same parameters in the options object.

If you want to use the length option for lru-cache, note that the memoized values are arrays: [exception, returnValue].

var memoizedFsReadFileSync = memoizeSync(require('fs').readFileSync, {
    max: 1000000,
    length: function (exceptionAndReturnValue) {
        if (exceptionAndReturnValue[0]) {
            return 1;
        } else {
            var body = exceptionAndReturnValue[1];
            return Buffer.isBuffer(body) ? body.length : Buffer.byteLength(body);
        }
    },
    maxAge: 1000
});

The LRU instance is exposed in the cache property of the memoized function in case you need to access it.

Installation

Make sure you have node.js and npm installed, then run:

npm install memoizesync

Browser compatibility

memoizeSync uses the UMD wrapper, so it should also work in browsers. You should also have the node-lru-cache included:

<script src="lru-cache.js"></script>
<script src="memoizeSync.js"></script>
<script>
    var memoizedFunction = memoizeSync(function () {
        // ...
    });
</script>

lru-cache uses Object.defineProperty and doesn't include an UMD wrapper, but if you define a shims config it should be possible to get it memoizeSync working with require.js, at least in newer browsers.

License

3-clause BSD license -- see the LICENSE file for details.