you just need to learn javascript, here is result please look into this i just store both into array, and then run loop and match and push into one.

    let firstarray =[
  {
    "addrSeq": "12",
    "accountMask": "********7479",
    "vpainfo": []
  },
  {
    "addrSeq": "13",
    "accountMask": "********74",
    "vpainfo": []
  }
]

let secondarray = [
  {
    "addrSeq": "12",
    "vpa": "saasasa@fff"
  },
  {
    "addrSeq": "12",
    "vpa": "xyz@com"
  },
  {
    "addrSeq": "13",
    "vpa": "saas@ddd"
  }
]
// merge both array into one using addrSeq match value 
let mergedarray = firstarray.map(function(item) {
    secondarray.map(function(item2) {
        if (item.addrSeq == item2.addrSeq) {
            item.vpainfo.push(item2);
        }
    });
  return item;
});

console.log(mergedarray);

You can achieve it via simple forEach loop.

Demo :

const array1 = [
  {
    "addrSeq": "12",
    "accountMask": "********7479",
    "vpainfo": []
  },
  {
    "addrSeq": "13",
    "accountMask": "********74",
    "vpainfo": []
  }
];

const array2 = [
  {
    "addrSeq": "12",
    "vpa": "saasasa@fff"
  },
  {
    "addrSeq": "12",
    "vpa": "xyz@com"
  },
  {
    "addrSeq": "13",
    "vpa": "saas@ddd"
  }
];

array2.forEach((obj) => {
    array1.forEach((array1Obj) => {
    if (obj.addrSeq === array1Obj.addrSeq) {
        array1Obj.vpainfo.push(obj.vpa)
    }
  });
});

console.log(array1);

Assuming that the OP requires Array1 to be updated such that each object's vpaIinfo array gets updated based on the data in Array2, the following solution may be one possible way to achieve the desired objective.

Code Snippet

const getUpdatedArr = (ar1, ar2) => (
  ar1.map(
    obj => ({
      ...obj,
      vpainfo: [
        ...obj.vpainfo,
        ...ar2.filter(
          ({addrSeq}) => (obj.addrSeq === addrSeq)
        ).map(
          ({vpa}) => vpa
        )
      ]
    })
  )
);

const arr1 = [
  {
    "addrSeq": "12",
    "accountMask": "********7479",
    "vpainfo": []
  },
  {
    "addrSeq": "13",
    "accountMask": "********74",
    "vpainfo": []
  }
];

const arr2 = [
  {
    "addrSeq": "12",
    "vpa": "saasasa@fff"
  },
  {
    "addrSeq": "12",
    "vpa": "xyz@com"
  },
  {
    "addrSeq": "13",
    "vpa": "saas@ddd"
  }
];

console.log(getUpdatedArr(arr1, arr2));

Explanation

• Iterate over array-1 using .map()
• For each object, keep the rest of the props as-is & manipulate only vpainfo
• Retain any existing values in current vpainfo (using ...obj.vpainfo)
• Append to this, any relevant vpa found in array-2
• The above is accomplished by using .filter() to retain only those with same addrSeq -AND- then, using .map() to extract just the vpa prop (using de-structuring)