Pushing checkbox values from one array to another

I have very little experience with JavaScript however I am attempting to write a function which pushes checkbox values from one array to another. I have written the following code, however it doesn't appear to work. Any help is appreciated.

var pages = document.forms['frm_list'].elements[ 'pages[]' ];
var selected = document.forms['frm_list'].elements[ 'selectedPages[]' ];
console.log(pages);
console.log(selected);


// using reference to sports obtained above
    for (var i=0, len=pages.length; i<len; i++) {
        pages[i].onclick = addPage;
    }

function addPage() {
    if ( this.checked ) {
        console.log(this);
        selected.push(pages);
        alert( this.value );
    } else {
        alert( this.value );
    }
}