前端项目实战56-判断result是否为空

if (result[splitKey[0]] === undefined) {
                // first operator for the key, we add it to the dict
                result[splitKey[0]] = op;
                console.log(result[splitKey[0]],"result---test1")
            }
            else {
              
                if (!Array.isArray(result[splitKey[0]])) {
                    // second operator, we transform to an array
                    result[splitKey[0]] = [result[splitKey[0]], op]
                    console.log(result[splitKey[0]],"result---test2")
                } else {
                    // third and subsequent, we add to array
                    result[splitKey[0]].push(op);
                    console.log(result[splitKey[0]],"result---test3")
                }
            }