Execute javascript directly in the HTTP response

Question

Some years ago I wrote a system where I'm pretty sure that I was able to execute javascript directly from the HTTP response.

What I did was to set the Content-Typeto application/javascript and then simply include the script in the response body.

Now I'm trying to do the same thing with just a simple alert: alert('Hello world'); as the HTTP response body. But the browser doesn't execute the script but just treats it as text.

Am I doing something wrong, or have it never been possible? (It's not an ajax request).

The browser expects HTML... Have you tried encapsulating the script in minimal HTML, including a <body onLoad="..."> ? — Roy Dictus
– Roy Dictus, Commented May 28, 2014 at 8:34
@RoyDictus: the Content-Type controls what the browser expects. — jgauffin
– jgauffin, Commented May 28, 2014 at 8:37

Community · Accepted Answer · 2017-05-23 12:05:07Z

4

This is how JSONP works. Simply add a <script /> tag, whose src is set to the remote script your want to execute, and you'll be good to go.

In your application:

var tag = document.createElement("script");

tag.src = "/your-remote-page/";
document.getElementsByTagName("head")[0].appendChild(tag);

/your-remote-page:

alert("Hi");

For more info on JSONP, see Can anyone explain what JSONP is, in layman terms?

If you have a response which conditionally returns either a file or a JavaScript response, then I'm not aware of a way you can either let the user download the file, or execute the JavaScript. The methods used to handle those responses are mutually exclusive. Either you inject a <script /> tag (for JavaScript), or submit a form/ anchor (file download).

edited May 23, 2017 at 12:05

CommunityBot

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answered May 28, 2014 at 8:34

Matt

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8 Comments

jgauffin Over a year ago

Not possible. The response is conditinal depending on the incoming data. It can either be a file or a javascript.

Cerbrus Over a year ago

@jgauffin: The response can either be a file or a JavaScript? That doesn't sound very consistent...

jgauffin Over a year ago

@Cerbrus: It's not my system. I'm just helping. There is a large calculation going on where some cases required additional verification from the user. They do not want to redo everything as the most common case generates the PDF.

Cerbrus Over a year ago

@jgauffin: "It's not my system": Yea, that explains that :-)

Matt Over a year ago

@jgauffin: If my answer isn't possible, then I'm AFAIK, you're out of options.

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