_promisify.js
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// freeze Array#slice, just in case of funny business later.
var _slice = Array.prototype.slice;
var getPromise = require('./_promise.js');
// deferred gets its own scope to prevent inadvertent capture in the closure
var deferred = function(options) {
var Promise = getPromise();
var resolve, reject, p = new Promise(function(_resolve, _reject) {
resolve = _resolve; reject = _reject;
});
var pattern = (options && options.pattern);
var noError = (options && options.noError);
var cb = pattern ? function(err) {
if (err && !noError) { return reject(err); }
var result = {}, i, offset = noError ? 0 : 1;
for (i = 0; i < pattern.length; i++) {
result[pattern[i]] = arguments[i+offset];
}
resolve(result);
} : noError ? resolve : function(err, val) {
if (err) { reject(err); } else { resolve(val); }
};
return { promise: p, callback: cb };
};
var promisify = module.exports = function(context, func, mandatoryArgs, options) {
if (options && options.callbackIsFirstArg) {
// duplicate some code here so we don't have to process this unusual
// situation at runtime in the common case.
return function(cb) {
if (typeof(cb) === 'function') {
return func.apply(context, arguments);
}
var d = deferred(options);
var a = _slice.call(arguments, 0);
a.unshift(d.callback);
func.apply(context, a);
return d.promise;
};
}
return function() {
var cb = arguments[arguments.length - 1];
if (typeof(cb) === 'function') {
return func.apply(context, arguments);
}
// ooh, promises.
var d = deferred(options);
var a = _slice.call(arguments, 0);
while (a.length < mandatoryArgs) { a.push(undefined); }
a.push(d.callback);
var retval = func.apply(context, a);
if (options && options.returnsObject) {
// it would be nice to have a better convention here
Object.defineProperty(retval, 'promise', { value: d.promise });
return retval;
}
return d.promise;
};
};