How to remove file with w2ui plugin

Question

I am using w2ui(http://w2ui.com/) plugin. I am using the upload model.

fields: [
        { name: 'taskName', type: 'text', required: true},
        { name: 'taskDomain', type: 'text', required: true},
        { name: 'mailList', type: 'file', accept:'.txt',options: formoptions('you can only upload file that ext txt',['txt']), required: true}
    ],
function formoptions (placehold,allowExt){
options = {
        selected        : [],       // selected array
        placeholder     : placehold,      
        max             : 0,        
        maxSize         : 0,       
        maxFileSize     : 0,        
        maxWidth        : 250,     
        maxHeight       : 350,    
        maxDropHeight   : 350,      
        silent          : true,    
        renderItem      : null,     
        style           : '',       
        onClick         : null,  
        onAdd           : function (event){
                            s =this;
                            for(var i in event){console.log(i)}
                            event.onComplete=function (argument) {
                                if(!isAllowUpload(event.file.name,allowExt)){
                                    //forbidden filetype
                                    w2alert('just allow'+String(allowExt)+'!');
                                    /***the question is here How do I remove this file***/
                                }
                               }
                            },     
        onRemove        : null,     
        onMouseOver     : null,     
        onMouseOut      : null      
};
return options;
}

I have some questions about using the w2ui upload model. When users uploads a file, we need to check the file to ensure the file type is permitted. How can I exclude files of a forbidden type?