Edit in JSFiddle

<script type="text/javascript">
	//배열 생성
	var array = ['포도','사과','바나나','망고'];
	            // 0       1      2       3
    document.write(array[0] + '<br>');
    document.write(array[1] + '<br>');
    document.write(array[2] + '<br>');
    document.write(array[3] + '<br>');
    
    document.write('======================<br>');
    
    var output = '';
    for(var i=0;i<array.length;i++){
    	output += i + ':' + array[i] + '<br>';
    }
   	document.write(output);
   	
   	document.write('======================<br>');
	var output2 = '';
	for(var i=array.length-1;i>=0;i--){
		output2 += i + ':' + array[i] + '<br>';
	}
	document.write(output2);
   
   	
    
</script>