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Return a value from a function using getJSON

in Using jQuery • 7 years ago

Hi,

I have a json file (detailing file extensions and their mime types)

I want to pass a function a file extension e.g. docx, return its associated mime type and to stop further searching through the json file

This is what I have so far but I'm getting undefined for mType in my function

var fileExt = "docx";
var mimeType = getMimeType(fileExt);
function getMimeType(fileExt) {
var mType;
$.getJSON('json/mimeTypes.json', function(data) {
$.each(data,function(key, value) {
if(key == fileExt) {
mType = value;
}
});
});
return mType;
}

Thanks in advance

Replies(6)

watusiware

Re: Return a value from a function using getJSON

7 years ago

I don't see anything wrong with your code. You must have some other problem.

But you don't need to "search" and you don't need the variable mType in any case.

var fileExt = 'docx';
var mimeType = getMimeType(fileExt);
function getMimeType(ext) {
$getJSON('json/mimeTypes.json', function(data) {
return data[ext];
)};
}

I changed the name of the function parameter above just to avoid confusing anybody who might think that the the function is accessing the fileExt variable.

A couple of thoughts:

- Is your "json" really json? You didn't show us a sample, so we don't know.

- Is your "json" on a server, or just in a local filesystem? Some browsers will not do Ajax with a local filesystem.

- Why go to the server to fetch this file every time you need to do this? I would just bake the data into the code. If you already have the data as JSON, that's easy, because JSON is a valid Javascript expression! Just copy the JSON string into your Javascript file, and assign it to a variable!

- Or, you can just retrieve the data ONCE and keep it around in a variable.

- Once you have retrieved a JSON file from a server and parsed it, FORGET IT WAS EVER JSON. Because once it is parsed, it is just an Javascript object. There is nothing special or different about it vs. any other Javascript object. JSON is just a way of encoding a complex data structure into a string so that it can be conveniently transported from A to B.