arr.reduce(callback(accumulator, currentValue[, index[, array]])[, initialValue])

var DICT_ARRAY= [
  {
    dictType: 718,
    dictParentCode: 'PROJECT_STAGE'
  },
  {
    dictType: 22,
    dictParentCode: 'OPP_CATEGORY'
  },
 
 
];
 let params = DICT_ARRAY.reduce((previousValue, item) => {
console.log('previousValue==',previousValue)
console.log('item==',item)
      if (previousValue) {
        previousValue = previousValue + '&';
      }
      return `${previousValue}typeAndParentCodes=${item.dictType}<@>${item.dictParentCode}`;
    }, '');
console.log('params==',params)
VM5388:14 previousValue== ''
VM5388:15 item== {dictType: 718, dictParentCode: "PROJECT_STAGE"}
VM5388:14 previousValue== typeAndParentCodes=718<@>PROJECT_STAGE
VM5388:15 item== {dictType: 22, dictParentCode: "OPP_CATEGORY"}
VM5388:21 params== typeAndParentCodes=718<@>PROJECT_STAGE&typeAndParentCodes=22<@>OPP_CATEGORY