IOperator example

const ioperator = require('ioperator'); const assert = require('assert'); const fs = require('fs'); // Pure descriptions of the various actions we're going to invoke. const readFile = (path, then) => ({ io: 'read-file', path, then }); const writeFile = (path, data, then) => ({ io: 'write-file', path, data, then }); // Pure function describing the impure actions required to read a file, // lower case its contents, and write it back out to another file const lowerCaseFile = (inp, out) => readFile(inp, contents => writeFile(out, contents.toString().toLowerCase(), _ => 'Go check ' + out) ); // // // Test with simulated actions // const simulatedActions = { 'read-file': io => '# Simulated file\n127.0.0.1 localhost bingo\n', 'write-file': io => 'Wrote to ' + io.path + ': ' + io.data // Act as if file was written }; ioperator .run(simulatedActions, lowerCaseFile('/etc/hosts', 'blah')) .then(result => assert.equal(result, 'Go check blah')); // // // Run with real actions // const realActions = { 'read-file': io => fs.readFileSync(io.path), 'write-file': io => fs.writeFileSync(io.path, io.data) }; ioperator .run(realActions, lowerCaseFile('/etc/hosts', '/tmp/hosts-lowercased')) .then(console.log) .catch(console.error);