如何更改表达式中的“结束日期”和“开始日期”

>我正在从服务器获取json数据，其中我得到的日期表达式为"t+1"，"t+2"，"t-1"。t 代表当前或系统日期。我需要更改这些表达式，如果t今天是日期 2016-03-14。那么t-1 2016-03-13.我们可以在javascript中更改这个表达式吗

这是我得到的对象输入

   [
      {
        "column": {
          "name": "a",
          "userId": "dipu"
        },
        "deal": {
          "dealNumbers": [],
          "fromDateExpression": {
            "expression": "t-1",
            "date": "2016-03-08"
          },
          "toDateExpression": {
            "expression": "t",
            "date": "2016-03-08"
          }
        }
      },
      {
        "column": {
          "name": "bb_test",
          "userId": "dipu"
        },
        "deal": {
          "dealNumbers": [
            "HH_2282825"
          ],
          "fromDateExpression": {
            "expression": "t+1",
            "date": "2016-03-09"
          },
          "toDateExpression": {
            "expression": "t+7",
            "date": "2016-03-17"
          }
        }
      },
      {
        "column": {
          "name": "my view",
          "userId": "dipu",
          "associatedWithAView": false
        },
        "deal": {
          "dealNumbers": [
            "HH_2282759"
          ],
          "fromDateExpression": {
            "expression": "t+2",
            "date": "2016-02-19"
          },
          "toDateExpression": {
            "expression": "t+3",
            "date": "2016-02-19"
          }
        }
      }
    ] 

我需要转换 json 数组.我这样尝试

https://jsfiddle.net/e4nt1doz/1/

function changeDatefromExpress(expr){
if(expr=="t"){
var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1; //January is 0!
var yyyy = today.getFullYear();
return yyyy-mm-dd
}else(expr=="t+1"){
}
}

预期输出是这样的

[
  {
    "column": {
      "name": "a",
      "userId": "dipu"
    },
    "deal": {
      "dealNumbers": [],
      "fromDateExpression": {
        "expression": "t-1",
        "date": "2016-03-13"
      },
      "toDateExpression": {
        "expression": "t",
        "date": "2016-03-14"
      }
    }
  },
  {
    "column": {
      "name": "bb_test",
      "userId": "dipu"
    },
    "deal": {
      "dealNumbers": [
        "HH_2282825"
      ],
      "fromDateExpression": {
        "expression": "t+1",
        "date": "2016-03-15"
      },
      "toDateExpression": {
        "expression": "t+7",
        "date": "2016-03-21"
      }
    }
  },
  {
    "column": {
      "name": "my view",
      "userId": "dipu",
      "associatedWithAView": false
    },
    "deal": {
      "dealNumbers": [
        "HH_2282759"
      ],
      "fromDateExpression": {
        "expression": "t+2",
        "date": "2016-03-16"
      },
      "toDateExpression": {
        "expression": "t+3",
        "date": "2016-02-17"
      }
    }
  }
]

我可以使用正则表达式吗？因为像t+5这样的案例很多，t+6