You can apply a Live Effect with settings you supply that won't invoke a dialog. Please have a look at my Live Effect functions for Illustrator repo. Its a free collection of functions that apply the Live Effects. So the one you would want is this one:
//@include 'LE.js'
var item = app.activeDocument.selection[0],
mm = 2.834645669;
LE_Feather(item, { radius: 5 * mm });
// from https://github.com/mark1bean/live-effect-functions-for-illustrator
function LE_Feather(item, options) {
try {
var defaults = {
radius: 10,
expandAppearance: false
}
var o = LE.defaultsObject(item, defaults, options, arguments.callee)
var xml = '<LiveEffect name="Adobe Fuzzy Mask"><Dict data="R Radius #1 "/></LiveEffect>'
.replace(/#1/, o.radius);
LE.applyEffect(item, xml, o.expandAppearance);
} catch (error) {
LE.handleError(error);
}
};
But it relies on another file "LE.js" which must be in the same folder as the script file (or you can target it with the include path of course). It's simplest to just download the whole release. Hope it helps.
- Mark