How to know if a SharePoint icon will appear as valid image?

Question

I have a web part that displays documents and the icon based on their extension (for example Word document displays Word logo based on .docx). I am building a url to display the image

extension = "docx"
var iconLocation = hostUrl + "/_layouts/15/image/ic" + extension + ".png";

I have found through researching this topic that txt extensions need to end with .gif instead of .png. Is there a way to know for sure which icons are supported? I ran into an issue where displaying .png files didn't show a valid image but I am unable to find some sort of documentation that would tell me which files will be handled and how (.png or .gif ending, possible others?)

Answer 1

Below are the list icons for different files. This has been extracted from On-Premises server. But these are being used same for SharePoint online site also.

You can see a list of your file extensions and support icon images with extension.

Answer 2

This is the code I use

function getIconUrl(extension, isLarge){

    var filename;

    extension = extension.toLowerCase();

    switch(extension){
        case 'pptx':
        case 'ppt':
        case 'docx':
        case 'doc':
        case 'xlsx':
        case 'xls':
        case 'pdf':
            filename='ic'+extension+'.png';
        break;

        case 'html':
        case 'htm':
            filename='ichtm.gif';
        break;

        case 'zip':
        case 'aspx':
        case 'asp':
            filename='ic'+extension+'.gif';
        break;

        default:
            filename='icgen.gif';

    }

    return '/_layouts/images/'+((isLarge) ? "lg_" : "")+filename;
}

I guess we don't have txt files, but this should help you work it out.