当心下面例子的循环：闭包中的局部变量可能和你最初想的不一样。

如题，这是为什么？

<script>
function buildList(list) {   
  var result = [];   
  for (var i = 0; i < list.length; i++) {   
    var item = 'item' + list[i];   
    result.push( function() {document.write(item + ' ' + list[i] + '<br />')} );   
  }   
  return result;   
}   

function testList() {   
  var fnlist = buildList([1,2,3]);   
  // using j only to help prevent confusion - could use i   
  for (var j = 0; j < fnlist.length; j++) {   
    fnlist[j]();   
  }   
}     

testList();  //输出3次：'item3 undefined' 
document.write('<br />');
</script>

 

评论

1 楼 Matrixes 2012-08-07  

<script>
function buildList(list) { 

  var result = [];   

  for (var k = 0; k < list.length; k++) {    

	result.push(

		function(i){	

			var item = 'item' + list[i];	
			
			return function(){

				document.write(item + ' ' + list[i] + '<br />');

			}

		}(k)

	);  

  } 
  
  return result;   

}   

function testList() {   

  var fnlist = buildList([1,2,3]);   

  // using j only to help prevent confusion - could use i   
  for (var j = 0; j < fnlist.length; j++) {   

    fnlist[j]();   

  } 
  
}     

testList(); 
</script>