A script to increase the minimum canvas size? (Like Fit Image, but with just my canvas)

Question

For starters to be clear, I'm looking to manipulate canvas size. Not image size.
I want to create a script to automatically increase the width and height of my canvas in Photoshop to a specific size when necessary. I only want this to happen if my canvas is less than that specified size. For example: Let's say my canvas size is 300x250. I want the canvas to be at LEAST 600x600. If I run my action it will increase the canvas size to 600x600 for me. If I run this same script on an image where the canvas size is already 700x700, it won't do anything at all to it because both the width and height are equal to or greater than my target size.
It would also need to work with the height and width on an individual basis. If my image is 400x800, the action would increase my width from 400 to 600, but it would leave the height of 800 alone. So the final canvas size will end up being 600x800.
It's kind of like the "Fit Image" option in Photoshop, but I only want to manipulate my canvas size, NOT my image size.

Answer 1

It is possible.
But if you hope that the dialog remembers the last settings that would require storing those values (which could be done with a txt-file at some pre-defined location), but it would make the Script a bit more complicated.
// resize canvas in either direction if it is below a defined minimum;
// 2011; use it at your own risk;
#target photoshop
if (app.documents.length > 0) {
// dialog;
var dlg = new Window("dialog", "increase width and height if under", [500,300,750,380]);
// filter for checking if entry is numeric, thanks to xbytor;
numberKeystrokeFilter = function() {
          if (this.text.match(/[^\-\.\d]/)) {
                    this.text = this.text.replace(/[^\d]/g, "")
          if (Number(this.text <= 0)) {this.text = 5};
          this.text = Math.round(Number(this.text));
// fields for entry;
dlg.hor = dlg.add("edittext", [14,15,88,35], "600", {multiline:false});
dlg.hor.onChange = numberKeystrokeFilter;
dlg.horText = dlg.add("statictext", [93,15,118,35], "px", {multiline:false});
dlg.ver = dlg.add("edittext", [129,15,210,35], "600", {multiline:false});
dlg.ver.onChange = numberKeystrokeFilter;
dlg.verText = dlg.add("statictext", [215,15,240,35], "px", {multiline:false});
dlg.hor.active = true;
// ok- and cancel-button;
dlg.buildBtn = dlg.add("button", [13,45,118,68], "OK", {name:"ok"});
dlg.cancelBtn = dlg.add("button", [128,45,240,68], "Cancel", {name:"cancel"});
// show dialog;
dlg.center();
// show dialog;
var myReturn = dlg.show ();
// proceed if ok-ed;
if (myReturn == 1) {
var myDocument = app.activeDocument;
// set to pixels;
var originalRulerUnits = app.preferences.rulerUnits;
app.preferences.rulerUnits = Units.PIXELS;
// set the minimum values;
var minWidth = Number(dlg.hor.text);
var minHeight = Number(dlg.ver.text);
// get current ones;
var theWidth = myDocument.width;
var theHeight = myDocument.height;
// resize canvas;
myDocument.resizeCanvas(Math.max(minWidth, theWidth), Math.max(minHeight, theHeight), AnchorPosition.MIDDLECENTER);
// reset;
app.preferences.rulerUnits = originalRulerUnits;