php?二维数组转一维数组

Array ( [0] => A1 [1] => A2 [2] => A3 [3] => A4 [4] => A5 ) 如何将这个数组转化为Array(A1,A2,A3,A4,A5)

for(var i=0;i<a.length;i++){                   alert(a[i]);                }循环出来的是 a  r  r  a  y 

<?php$a = array( 'A1', 'A2', 'A3', 'A4', 'A5' );?><script>var a = <?php echo json_encode($a); ?>;for(var i=0;i<a.length;i++){  alert(a[i]);}</script>

<?php$a = array( 'A1', 'A2', 'A3', 'A4', 'A5' );?><script>var a = Array("<?php echo join('", "', $a); ?>");for(var i=0;i<a.length;i++){  alert(a[i]);}</script>