memolite

Extremely simple memoizing for async functions. It is available through npm

npm install memolite

Usage

memolite memoizes async functions on the form function(callback) { ... }

var memolite = require('memolite');
var fs = require('fs');
 
var random = memolite(function(callback) {
    console.log('I am only called once');
    setTimeout(function() {
        callback(Math.random());
    }, 1000);
});
 
random(function(num) {
    console.log(num); // prints a random number after 1s
});
 
random(function(num) {
    console.log(num); // prints the same number as above
});

If you wanted to do a file reader that only read files once and remembered the result you would do

var memolite = require('memolite');
var fs = require('fs');
 
var fileReader = function(filename) {
    return memolite(function(callback) {
        console.log('reading '+filename);
        fs.readFile(filename, callback);
    });
};
 
var readReadme = fileReader('README.md');
 
readReadme(function(err, data) { // prints 'reading README.md'
    console.log('README is '+data);
});
 
readReadme(function(err, data) { // memolite will wait for the read to finish and return the data
    console.log('README is '+data);
});

If an error is passed to the callback then memolite will not remember the result

var run = memolite(function(callback) {
    console.log('running');
    callback(new Error('bad things'));
});
 
run(function(err) { // 'running' is printed
    console.log(err);
});
 
run(function(err) { // 'running' is printed again
    console.log(err);
});

A great usecase for memolite is doing lazy operations.

var makeFolder = memolite(function(callback) {
    fs.mkdir('/tmp/my-folder', callback);
});
 
var writeFile = function(filename, data, callback) {
    makeFolder(function(err) {
        if (err) return callback(err);
        fs.writeFile('/tmp/my-folder/'+filename, data, callback);
    });
};

Calling writeFile multiple times would result in fs.mkdir(...) being called only once (if there are no errors).

License

MIT