---
layout: api
id: promise.promisify
title: Promise.promisify
---
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<div class="api-code-section"><markdown>
##Promise.promisify
```js
Promise.promisify(
function(any arguments..., function callback) nodeFunction,
[Object {
multiArgs: boolean=false,
context: any=this
} options]
) -> function
```
Returns a function that will wrap the given `nodeFunction`. Instead of taking a callback, the returned function will return a promise whose fate is decided by the callback behavior of the given node function. The node function should conform to node.js convention of accepting a callback as last argument and calling that callback with error as the first argument and success value on the second argument.
If the `nodeFunction` calls its callback with multiple success values, the fulfillment value will be the first fulfillment item.
Setting `multiArgs` to `true` means the resulting promise will always fulfill with an array of the callback's success value(s). This is needed because promises only support a single success value while some callback API's have multiple success value. The default is to ignore all but the first success value of a callback function.
If you pass a `context`, the `nodeFunction` will be called as a method on the `context`.
Example of promisifying the asynchronous `readFile` of node.js `fs`-module:
```js
var readFile = Promise.promisify(require("fs").readFile);
readFile("myfile.js", "utf8").then(function(contents) {
return eval(contents);
}).then(function(result) {
console.log("The result of evaluating myfile.js", result);
}).catch(SyntaxError, function(e) {
console.log("File had syntax error", e);
//Catch any other error
}).catch(function(e) {
console.log("Error reading file", e);
});
```
Note that if the node function is a method of some object, you can pass the object as the second argument like so:
```js
var redisGet = Promise.promisify(redisClient.get, {context: redisClient});
redisGet('foo').then(function() {
//...
});
```
But this will also work:
```js
var getAsync = Promise.promisify(redisClient.get);
getAsync.call(redisClient, 'foo').then(function() {
//...
});
```
</markdown></div>
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