How do I stop running a script when I hit cancel on dialog box

var dialogResponse; // init variable
function mainScript() {
    showDialog();
    if (dialogResponse == "cancel") return;
    //... otherwise, do some stuff
}
function showDialog() {
    var dlg = new Window('dialog');
    
    buttonOk = dlg.add('button', undefined, 'Ok')  
    buttonOk.onClick = function(){
        dlg.close();
        dialogResponse = "ok"
    }  
    dlg.cancelBtn = dlg.add('button',undefined,'Cancel');
    dlg.cancelBtn.onClick = function(){
        dlg.close();
        dialogResponse = "cancel"
    }
    
    g.center(), g.show();
}

If you want to cancel the script when you hit the cancel button, put your code either in a function or an if clause that checks to see if the cancel button was pressed (have a onClick function set a variable, such as "run" to false to do this.

var run = true
var dlg = new Window('dialog')
dlg.cancelBtn = dlg.add('button',undefined,'Cancel')
dlg.cancelBtn.onClick = function(){run = false}
if(run){
    //your code
    }