Edit in JSFiddle

var aArray = [ 1, 2, 3, 4 ];
var bArray = [ 5, 6, 7, 8 ];
var cArray = [ 9, 10, 11, 12];
var allArray = aArray.concat( bArray ).concat( cArray );

document.write( "<li>" + allArray + "</li>" );

//같은 배열객체로도 사용 가능
var duplicationArray = aArray.concat( aArray );
document.write( "<li>" + duplicationArray + "</li>" );