javascript简单循环

Question

var friends = ["Miha", "Artur", "Karen", "zollex"];
var len = friends.length;
var friend = 0;
var msg = '';
var i;
for (i = 0; i <len; i++){ 
  friend = (i + 1);
  msg+= "Friend number " + friend + ":";
  msg+=friends[i] + "<br />";
  document.write(msg);
}

我上面写的代码如下.结果如下:

朋友1:Miha
朋友1号:Miha
朋友2号:Artur
朋友1号:Miha
朋友2号:Artur
朋友3号:Karen
朋友1号:Miha
朋友2号:Artur
朋友3号:Karen
朋友4号:zollex

虽然应该只有4个朋友.我真的好奇为什么document.write多次重复这个名字.

Answer 1

因为您在每次迭代时使用+ =构建字符串,并且您不会在每次迭代时重置它.

msg += "Friend number " + friend + ":";
    ^^
msg += friends[i] + "<br />";
    ^^

移动document.writefor循环外部或msg在每次迭代时将其设置为空.

var friends = ["Miha", "Artur", "Karen", "zollex"];
var len = friends.length;
var friend = 0;
var msg = '';
var i;
for (i = 0; i <len; i++){ 
  friend = (i + 1);
  msg += "Friend number " + friend + ":";
  msg += friends[i] + "<br />";
}
document.write(msg);