Photoshop JS script for quickly exporting selection to PNG.

selection2PNG.jsx

app.displayDialogs = DialogModes.NO;

var pngSaveOptions = new PNGSaveOptions();
pngSaveOptions.compression = 9;
pngSaveOptions.interlaced = false;

var hasSelection;
var docRef;
var artLayer;
var width = app.activeDocument.width;
var height = app.activeDocument.height;

try {
    hasSelection = !!app.activeDocument.selection.bounds;    
} catch (err) {
    hasSelection = false;
}

if (hasSelection) {
    //copy merged
    app.activeDocument.selection.copy(true);

    //create new RGB document with transperant background
    docRef = app.documents.add(width, height, 72, null, NewDocumentMode.RGB, DocumentFill.TRANSPARENT)
    artLayer = docRef.paste();
    
    //crop the image to pasted bounds
    docRef.crop(artLayer.bounds);
} else {
    docRef = app.activeDocument;
}

var file = File.saveDialog("Export as PNG to...");
if (file && ((file.exists && confirm("Overwrite " + file +"?")) || !file.exists)) {
    docRef.saveAs(file, pngSaveOptions, !hasSelection, Extension.LOWERCASE);
    if (hasSelection) {
    docRef.close(SaveOptions.DONOTSAVECHANGES);
    }
}