Add util.promisify and util.callbackify

package.json

@@ -29,6 +29,7 @@
   "license": "MIT",
   "devDependencies": {
     "airtap": "0.0.6",
+    "is-async-supported": "~1.2.0",
     "run-series": "~1.1.4",
     "tape": "~4.9.0"
   },

test/browser/callbackify.js

@@ -0,0 +1,169 @@
+'use strict';
+
+var test = require('tape');
+var callbackify = require('../../').callbackify;
+
+if (typeof Promise === 'undefined') {
+  console.log('no global Promise found, skipping callbackify tests');
+  return;
+}
+
+function after (n, cb) {
+  var i = 0;
+  return function () {
+    if (++i === n) cb();
+  }
+}
+
+var values = [
+  'hello world',
+  null,
+  undefined,
+  false,
+  0,
+  {},
+  { key: 'value' },
+  function ok() {},
+  ['array', 'with', 4, 'values'],
+  new Error('boo')
+];
+if (typeof Symbol !== 'undefined') {
+  values.push(Symbol('I am a symbol'));
+}
+
+test('util.callbackify resolution value is passed as second argument to callback', function (t) {
+  var end = after(values.length * 2, t.end);
+  // Test that the resolution value is passed as second argument to callback
+  values.forEach(function(value) {
+    // Test Promise factory
+    function promiseFn() {
+      return Promise.resolve(value);
+    }
+
+    var cbPromiseFn = callbackify(promiseFn);
+    cbPromiseFn(function(err, ret) {
+      t.ifError(err);
+      t.strictEqual(ret, value, 'cb ' + typeof value);
+      end();
+    });
+
+    // Test Thenable
+    function thenableFn() {
+      return {
+        then: function(onRes, onRej) {
+          onRes(value);
+        }
+      };
+    }
+
+    var cbThenableFn = callbackify(thenableFn);
+    cbThenableFn(function(err, ret) {
+      t.ifError(err);
+      t.strictEqual(ret, value, 'thenable ' + typeof value);
+      end();
+    });
+  });
+});
+
+test('util.callbackify rejection reason is passed as first argument to callback', function (t) {
+  var end = after(values.length * 2, t.end);
+  // Test that rejection reason is passed as first argument to callback
+  values.forEach(function(value) {
+    // test a Promise factory
+    function promiseFn() {
+      return Promise.reject(value);
+    }
+
+    var cbPromiseFn = callbackify(promiseFn);
+    cbPromiseFn(function(err, ret) {
+      t.strictEqual(ret, undefined, 'cb ' + typeof value);
+      if (err instanceof Error) {
+        if ('reason' in err) {
+          t.ok(!value);
+          t.strictEqual(err.message, 'Promise was rejected with a falsy value');
+          t.strictEqual(err.reason, value);
+        } else {
+          t.strictEqual(String(value).slice(-err.message.length), err.message);
+        }
+      } else {
+        t.strictEqual(err, value);
+      }
+      end();
+    });
+
+    // Test Thenable
+    function thenableFn() {
+      return {
+        then: function (onRes, onRej) {
+          onRej(value);
+        }
+      };
+    }
+
+    var cbThenableFn = callbackify(thenableFn);
+    cbThenableFn(function(err, ret) {
+      t.strictEqual(ret, undefined, 'thenable ' + typeof value);
+      if (err instanceof Error) {
+        if ('reason' in err) {
+          t.ok(!value);
+          t.strictEqual(err.message, 'Promise was rejected with a falsy value');
+          t.strictEqual(err.reason, value);
+        } else {
+          t.strictEqual(String(value).slice(-err.message.length), err.message);
+        }
+      } else {
+        t.strictEqual(err, value);
+      }
+      end();
+    });
+  });
+});
+
+test('util.callbackify arguments passed to callbackified function are passed to original', function (t) {
+  var end = after(values.length, t.end);
+  // Test that arguments passed to callbackified function are passed to original
+  values.forEach(function(value) {
+    function promiseFn(arg) {
+      t.strictEqual(arg, value);
+      return Promise.resolve(arg);
+    }
+
+    var cbPromiseFn = callbackify(promiseFn);
+    cbPromiseFn(value, function(err, ret) {
+      t.ifError(err);
+      t.strictEqual(ret, value);
+      end();
+    });
+  });
+});
+
+test('util.callbackify `this` binding is the same for callbackified and original', function (t) {
+  var end = after(values.length, t.end);
+  // Test that `this` binding is the same for callbackified and original
+  values.forEach(function(value) {
+    var iAmThis = {
+      fn: function(arg) {
+        t.strictEqual(this, iAmThis);
+        return Promise.resolve(arg);
+      },
+    };
+    iAmThis.cbFn = callbackify(iAmThis.fn);
+    iAmThis.cbFn(value, function(err, ret) {
+      t.ifError(err);
+      t.strictEqual(ret, value);
+      t.strictEqual(this, iAmThis);
+      end();
+    });
+  });
+});
+
+test('util.callbackify non-function inputs throw', function (t) {
+  // Verify that non-function inputs throw.
+  ['foo', null, undefined, false, 0, {}, typeof Symbol !== 'undefined' ? Symbol() : undefined, []].forEach(function(value) {
+    t.throws(
+      function() { callbackify(value); },
+      'The "original" argument must be of type Function'
+    );
+  });
+  t.end();
+});

test/browser/index.js

@@ -1,2 +1,4 @@
 require('./inspect');
 require('./is');
+require('./promisify');
+require('./callbackify');

test/browser/promisify.js

@@ -0,0 +1,205 @@
+var promisify = require('../../').promisify;
+var test = require('tape');
+
+var hasSymbol = typeof Symbol !== 'undefined';
+
+if (typeof Promise === 'undefined') {
+  console.log('no global Promise found, skipping promisify tests');
+  return;
+}
+
+var callbacker = function (arg, cb) {
+  setTimeout(function () {
+    if (typeof arg === 'string')
+      cb(null, arg.toUpperCase());
+    else cb(new TypeError('incorrect type'));
+  }, 5);
+}
+var promiser = promisify(callbacker);
+
+test('util.promisify resolves', function (t) {
+  var promise = promiser(__filename);
+  t.ok(promise instanceof Promise);
+  promise.then(function (value) {
+    t.deepEqual(value, __filename.toUpperCase());
+    t.end();
+  });
+});
+
+test('util.promisify rejects', function (t) {
+  var promise = promiser(42);
+  promise.catch(function (error) {
+    t.equal(error.message, 'incorrect type');
+    t.end();
+  });
+});
+
+test('util.promisify custom', { skip: !hasSymbol }, function (t) {
+  function fn() {}
+  function promisifedFn() {}
+  fn[promisify.custom] = promisifedFn;
+  t.strictEqual(promisify(fn), promisifedFn);
+  t.strictEqual(promisify(promisify(fn)), promisifedFn);
+  t.end();
+});
+
+test('util.promisify custom of invalid type', { skip: !hasSymbol }, function (t) {
+  function fn2() {}
+  fn2[promisify.custom] = 42;
+  t.throws(
+    function () { promisify(fn2); },
+    /must be of type Function/
+  );
+  t.end();
+});
+
+test('util.promisify multiple callback values', function (t) {
+  function fn5(callback) {
+    callback(null, 'foo', 'bar');
+  }
+  promisify(fn5)().then(function (value) {
+    t.strictEqual(value, 'foo');
+    t.end();
+  });
+});
+
+test('util.promisify no callback success value', function (t) {
+  function fn6(callback) {
+    callback(null);
+  }
+  promisify(fn6)().then(function (value) {
+    t.strictEqual(value, undefined);
+    t.end();
+  });
+});
+
+test('util.promisify no callback arguments at all', function (t) {
+  function fn7(callback) {
+    callback();
+  }
+  promisify(fn7)().then(function (value) {
+    t.strictEqual(value, undefined);
+    t.end();
+  });
+});
+
+test('util.promisify passing arguments', function (t) {
+  function fn8(err, val, callback) {
+    callback(err, val);
+  }
+  promisify(fn8)(null, 42).then(function (value) {
+    t.strictEqual(value, 42);
+    t.end();
+  });
+});
+
+test('util.promisify passing arguments (rejects)', function (t) {
+  function fn9(err, val, callback) {
+    callback(err, val);
+  }
+  promisify(fn9)(new Error('oops'), null).catch(function (err) {
+    t.strictEqual(err.message, 'oops');
+    t.end();
+  });
+});
+
+test('util.promisify chain', function (t) {
+  function fn9(err, val, callback) {
+    callback(err, val);
+  }
+
+
+  Promise.resolve()
+    .then(function () { return promisify(fn9)(null, 42); })
+    .then(function (value) {
+      t.strictEqual(value, 42);
+      t.end();
+    });
+});
+
+test('util.promisify keeps correct `this`', function (t) {
+  var o = {};
+  var fn10 = promisify(function(cb) {
+
+    cb(null, this === o);
+  });
+
+  o.fn = fn10;
+
+  o.fn().then(function(val) {
+    t.ok(val);
+    t.end();
+  });
+});
+
+test('util.promisify calling callback multiple times', function (t) {
+  var err = new Error('Should not have called the callback with the error.');
+  var stack = err.stack;
+
+  var fn11 = promisify(function(cb) {
+    cb(null);
+    cb(err);
+  });
+
+  Promise.resolve()
+    .then(function () { return fn11(); })
+    .then(function () { return Promise.resolve(); })
+    .then(function () {
+      t.strictEqual(stack, err.stack);
+      t.end();
+    });
+});
+
+// Can't do this without Symbol() unfortunately
+test('util.promisify promisifying a promisified function', { skip: !hasSymbol }, function (t) {
+  function c() { }
+  var a = promisify(function() { });
+  var b = promisify(a);
+  t.notStrictEqual(c, a);
+  t.strictEqual(a, b);
+  t.end();
+});
+
+test('util.promisify sync throw becomes rejection', function (t) {
+  var errToThrow;
+  var thrower = promisify(function(a, b, c, cb) {
+    errToThrow = new Error();
+    throw errToThrow;
+  });
+  thrower(1, 2, 3)
+    .then(t.fail)
+    .then(t.fail, function (e) {
+      t.strictEqual(e, errToThrow);
+      t.end();
+    });
+});
+
+test('util.promisify callback and sync throw', function (t) {
+  var err = new Error();
+
+  var a = promisify(function (cb) { cb(err) })();
+  var b = promisify(function () { throw err; })();
+
+  Promise.all([
+    a.then(t.fail, function(e) {
+      t.strictEqual(err, e);
+    }),
+    b.then(t.fail, function(e) {
+      t.strictEqual(err, e);
+    })
+  ]).then(function () {
+    t.end();
+  });
+});
+
+test('util.promisify throws for incorrect argument types', function (t) {
+  var array = [undefined, null, true, 0, 'str', {}, []];
+  if (typeof Symbol !== 'undefined') array.push(Symbol());
+  array.forEach(function (input) {
+    t.throws(
+      function () { promisify(input); },
+      'The "original" argument must be of type Function'
+    );
+  });
+  t.end();
+});