SOURCE

const data=[
        {
          "name": "A",
          "children": [
            {
              "name": "A1",
              "children": [
                {
                  "name": "A11",
                  "children": null
                },
                {
                  "name":"A12",
                  "children": [
                    {
                      "name": "A121",
                      "children": null
                    }
                  ]
                },
                {
                  "name": "A13",
                  "children": [
                    {
                      "name": "A131",
                      "children": null
                    }
                  ]
                }
              ]
            },
            {
              "name": "A2",
              "children": [
                {
                  "name": "A21",
                  "children": null
                }]
            },
            {
              "name": "A3",
              "children": null
            },
            {
              "name": "A4",
              "children": null
            }
          ]
        },
        {
          "name": "B",
          "children": [
            {
              "name":"B1",
              "children": null
            }
          ]
        },  
        {
          "name": "C",
          "children":null
        }
      ];






// 设置每个节点的统计字段,并返回所有节点总数。
var toTreeCount = (data=[], countField='count')=>data.reduce((total,cur)=>(total+(cur[countField] = toTreeCount(cur.children||[], countField))),data.length);
console.log(toTreeCount(data,'childCount'));
console.log(data);

/*
function getLeafCountTree(json) {
            if(json.children ==null || json.children.length == 0){
                json.colspan = 1;
                return 1;
            }else{
                var leafCount = 0;
                for(var i = 0 ; i < json.children.length ; i++){
                    leafCount = leafCount + getLeafCountTree(json.children[i]);
                }
                json.colspan = leafCount;
                return leafCount;
            }
        }

      console.log(getLeafCountTree(data))  */