javascript - 将数组转换为树

Question

有人可以解释这段代码吗？我不明白“for”结构中的内容。

 var tree = {}

function addToTree(tree, array) { 
   for (var i = 0, length = array.length; i < length; i++) {
       tree = tree[array[i]] = tree[array[i]] || {}
   }
}

addToTree(tree, ["a", "b", "c"])
addToTree(tree, ["a", "b", "d"])

/*{
    "a": {
        "b": {
            "c": {},
            "d": {}
        }
    }
}*/

Answer 1

我扩展了 for 循环的主体并添加了一些注释，试图使事情更加明确。

for (var i = 0, length = array.length; i < length; i++) {
   // Assign the current item in the array to a variable
   var current = array[i];

   // If there is no property on the "tree" object corresponding to the value of 
   // "current", set this property to a new object
   if (!tree[current]) {
      tree[current] = {};
   }

   // Set the "tree" variable to the field in the "tree" object whose 
   // name corresponds to "current". On the next loop iteration, "tree" will
   // refer to this "child" object, resulting in a tree-like object being
   // created as we iterate.
   tree = tree[current];
}