把以下代码复制到你的公用js库中：
var ModalDialogWindow = function() {
    this.constructor();
    this.window = Ext.extend(Ext.Window,{
        closeable:true,
        closeAction:'close',
        draggable:true, 
        plain:true, 
        modal:true 
    });
}
ModalDialogWindow.prototype.initialize = function(obj) { 
    if(!IsArray(obj)) { 
        if (typeof(obj) == 'string') { 
            obj = obj.split(';'); 
            for(var i = 0; i < obj.length; i++) { 
                obj = obj.split(':'); 
                switch(obj[0]) { 
                    case 'dialogHeight': this.dialogHeight = parseInt(obj[1]);break; 
                    case 'dialogWidth': this.dialogWidth = parseInt(obj[1]);break; 
                    case 'dialogLeft': this.dialogLeft = parseInt(obj[1]);break; 
                    case 'dialogTop': this.dialogTop = parseInt(obj[1]);break; 
                    case 'resizable': this.resizable = obj[1];break; 
                    case 'scroll': this.scroll = obj[1];break; 
                    case 'title': this.title = obj[1];break; 
                } 
           } 

        } else if(typeof(obj) == 'object') { 
            for(var index in obj) { 
                switch(index) { 
                    case 'dialogHeight': this.dialogHeight = parseInt(obj[index]);break; 
                    case 'dialogWidth': this.dialogWidth = parseInt(obj[index]);break; 
                    case 'dialogLeft': this.dialogLeft = parseInt(obj[index]);break; 
                    case 'dialogTop': this.dialogTop = parseInt(obj[index]);break; 
                    case 'resizable': this.resizable = obj[index];break; 
                    case 'scroll': this.scroll = obj[index];break; 
                    case 'title': this.title = obj[index];break; 
                } 
            } 
        } 
    }
};
ModalDialogWindow.prototype.constructor = function() { 
    this.obj = this; 
    this.returnValue = null; 
    this.win = {}; 
    // showModalDialog arguments 
    this.sURL = ''; 
    this.dialogArguments = null; 
    //sFeatures arguments 
    this.dialogHeight = 100; 
    this.dialogWidth = 100; 
    this.dialogLeft = 0; 
    this.dialogTop = 0; 
    this.resizable = false; 
    this.scroll = true; 
    this.title = ''; 
    this.html = '';
};
ModalDialogWindow.prototype.destroy = function() { 
    this.constructor.call(this);
}
ModalDialogWindow.prototype.showModalDialog = function(sURL,vArguments,sFeatures) { 
    if(this.sURL != '') {this.destroy()} 
    this.sURL = sURL; 
    if(arguments.length < 3) {sFeatures = vArguments;vArguments = null;} 
    this.dialogArguments = vArguments?vArguments:null; 
    this.initialize(sFeatures); 
    window.win = this.obj; 
    this.html = '<iframe id="mdFrame" name="mdFrame" width="' + this.dialogWidth + '" height="' + this.dialogHeight + '" frameborder="0" src="' + this.sURL + '"></iframe>'; 
    this.win = new this.window({ 
        id: 'mdWin', 
        title: this.title, 
        resizable: this.resizable, 
        autoHeight: this.scroll, 
        width: this.dialogWidth, 
        height: this.dialogHeight, 
        html: this.html 
    }); 
    if(this.dialogLeft && this.dialogTop) {this.win.setPosition(this.dialogLeft,this.dialogTop);} 

    this.win.addListener({ 
        'show':function() {}, 
        'close':function() {window.win = null;} 
    }); 

    this.win.show();
};

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父页面调用代码：
<input name="test" type="text" />
function getValue(obj) { 
    var _win = new ModalDialogWindow(); 
    _win.showModalDialog('sub.html','','title:test;dialogWidth:600;dialogHeight:400'); 
    _win.win.on('beforeclose',function(){ 
        obj.value = _win.returnValue; 
    });
}

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子页面传值变量：
<script>parent.win.returnValue = '要传的变量'</script>

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有什么可改进的地方还请大家指点