Code transformer to change Node-style callbacks into promises.
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Promise Me Build Status

Promise Me helps you move your code from using callbacks to using promises, for example through Q, RSVP.js or when.js.

It parses your code and then manipulates the AST to transform the callbacks into calls to then(), including a rejection handler if you handle the original callback error. Think of it as a slightly smarter find-and-replace. It will probably break your code and require you to fix it.

Try the live demo!

Installation and usage

$ npm install -g promise-me
$ promise-me script.js

API

var promiseMe = require("promise-me");

var before = "...";
var after = promiseMe.convert(before, options);

promiseMe.convert(code, options)

Convert the given code to use promises.

  • {string} code String containing Javascript code.
  • {Object} options Options for generation.
  • {Object} options.parse Options for esprima.parse. See http://esprima.org/doc/ .
  • {Object} options.generate Options for escodegen.generate. See https://github.com/Constellation/escodegen/wiki/API .
  • {Function} options.matcher A function of form (node) => boolean. Must accept any type of node and return true if it should be transformed into then, using the replacer, and false if not. See https://developer.mozilla.org/en-US/docs/SpiderMonkey/Parser_API for node types.
  • {Function} options.replacer A function of form (node) => Node. Must accept any type of node and return a new node to replace it that uses then instead of a callback. Will only get called if options.matcher returns true. See https://developer.mozilla.org/en-US/docs/SpiderMonkey/Parser_API for node types.
  • {Function} options.flattener A function of form (node) => Node. Must accept any type of node, and return either return the original node, or a new node with the then calls flattened.
  • {Function} log Function to call with log messages.
  • Returns {string} The Javascript code with callbacks replaced with .then() functions.

Examples

Simple callback

Before:

getDetails("Bob", function (err, details) {
    console.log(details)
});

After:

getDetails('Bob').then(function (details) {
    console.log(details);
});

Error handling

Before:

getDetails("Bob", function (err, details) {
    if (err) {
        console.error(err);
        return;
    }
    console.log(details)
});

After:

getDetails('Bob').then(function (details) {
    console.log(details);
}, function (err) {
    console.error(err);
    return;
});

Nested callbacks

Before:

getDetails("Bob", function (err, details) {
    getLongLat(details.address, details.country, function(err, longLat) {
        getNearbyBars(longLat, function(err, bars) {
            console.log("Your nearest bar is: " + bars[0]);
        });
    });
});

After:

getDetails('Bob').then(function (details) {
    return getLongLat(details.address, details.country);
}).then(function (longLat) {
    return getNearbyBars(longLat);
}).then(function (bars) {
    console.log('Your nearest bar is: ' + bars[0]);
});

Captured variables

Before:

getDetails("Bob", function (err, details) {
    getLongLat(details.address, details.country, function(err, longLat) {
        getNearbyBars(longLat, function(err, bars) {
            // Note the captured `details` variable
            console.log("The closest bar to " + details.address + " is: " + bars[0]);
        });
    });
});

After:

getDetails("Bob").then(function (details) {
    getLongLat(details.address, details.country).then(function (longLat) {
        return getNearbyBars(longLat);
    }).then(function (bars) {
        // Note the captured `details` variable
        console.log("The closest bar to " + details.address + " is: " + bars[0]);
    });
});