Illustrator script that creates a palette with a slider that allows you to scale the stroke width of the selected object. Written by Carlos Canto and posted in the Illustrator scripting forums. What's remarkable about this file is the streamlining of the BridgeTalk call, which allows the palette to execute functions while staying open.

ScaleStrokePalette.js

// script.name = scaleStrokes.jsx;
// script.description = scales selected objects strokes only;
// script.required = one or more selected objects
// script.parent = CarlosCanto // 5/7/12;
// script.elegant = false;
// script.updates = preview ON by default // 5/7/12
#target Illustrator
#targetengine 'main'

var unscale = 0;

var win = new Window("palette", "Scale Strokes");
var pnlScale = win.add("panel");
pnlScale.orientation = "row";
var lblScale = pnlScale.add("statictext", undefined, "Scale");
var editScale = pnlScale.add("edittext", undefined, "100");
editScale.characters = 5;
var lblScale = pnlScale.add("statictext", undefined, "%");

var grpScroll = win.add("group");
var scrlScale = grpScroll.add("scrollbar", undefined, 100, 1, 1000); // 1 min scaling to avoid division by zero
var btnReset = win.add("button", undefined, "Reset");
btnReset.helpTip = "unscale or reset value to 100%"
win.helpTip = "\u00A9 2012 Carlos Canto";

scrlScale.onChange = function() {
  editScale.text = this.value; // update edit box with scroll value
	editScale.notify("onChange") // call the onchange event handler
}

editScale.onChange = function() {
	if (this.text < 1) // if value entered by hand is less than 1, make it 1 to avoid division by zero
	this.text = 1;
	scrlScale.value = this.text; // update edit box with scroll value
	btMsg("scaleStrokes(activeDocument.selection," + editScale.text + ")");
}

// unscale (back to 100%) on reset, except no scaling has applied
btnReset.onClick = function() {
	editScale.text = 100;
	editScale.notify("onChange")
}

// Deal with selection changed, reset values onActivate
var sel, newsel;

win.onDeactivate = function() {
	btMsg('sel = activeDocument.selection')
}

win.onActivate = function() {
	btMsg('newsel = activeDocument.selection')
	if (!isSelEqual(sel, newsel) && editScale.text != 100) {
		editScale.text = scrlScale.value = 100, unscale = 0;
	}
}

win.center();
win.show();

function scaleStrokes(sel, scale) {
	// skip unscaling the first time, there's nothing to unscale
	if (unscale != 0) {
		unscaleStrokes(sel, unscale);
	}
	for (i = 0; i < sel.length; i++) {
		var pgitem = sel[i];
		pgitem.resize(100, 100, undefined, undefined, undefined, undefined, scale, Transformation.CENTER);
	}
	unscale = 10000 / scale;
}

// unscale or bring back selection to 100%
function unscaleStrokes(sel, unscale) {
	for (j = 0; j < sel.length; j++) {
		var pgitem = sel[j];
		pgitem.resize(100, 100, undefined, undefined, undefined, undefined, unscale, Transformation.CENTER);
	}
}

function BridgeTalkErrorHandler(a) {
	alert(a.body + "(" + a.headers["Error-Code"] + ")")
}

// use BridgeTalk to call function, this is needed because the use of "palette" panel
function btMsg(a) {
	var b = new BridgeTalk;
	b.target = "illustrator", b.body = a, b.onError = BridgeTalkErrorHandler, b.send()
}

// check whether selection changed or not
function isSelEqual(a, b) {
	if (!a || !b) return false
	if (a.length != b.length) return false
	for (var i = 0; i < a.length; i++) {
		if (a[i] != b[i]) return false
	}
	return true
}