dude, if you ask questions, you should type the code well, otherwise it looks very messy and you are not in the mood to answer questions. I've already lined up for you.

look at your problem, it should be to merge the two arrays into one array according to the sequence number. Your method is problematic, because each time you loop arr01 to the last element, and then change the data in arr02 .

map function returns a new array, so instead of nesting map , just loop and reassemble the array.

refer to this:

var arr = [];
arr01.forEach(function(value, index) {
    //  arr02  city
    value.city = arr02[index] || '';
    arr.push(value)
})
console.log(arr)

or:

var arr = [];
arr02.forEach(function(value, index) {
    //  arr01  acdount
    value.account = arr01[index] || '';
    arr.push(value)
})
console.log(arr)

if you modify the problem, you want each to be modified accordingly, so nest the loop twice. Instead of using map , you can directly use forEach .

var arr = [];
arr01.forEach(function(v, i) {
    arr02.forEach(function(vv, ii) {
        arr.push({
            account: v.account,
            city: vv.city
        })
    })
})
console.log(arr)

what you have changed is the reference address of the object. All the effects of the last change have been entered by the previous push

var newArr = [];
arr01.forEach(v1 => {
    arr02.forEach(v2 => {
        newArr.push(Object.assign({}, v2, {
            account: v1.account
        }))
    })
})
console.log(newArr)

map is an array. For this problem, forEach is more appropriate

let newArr = [];
arr01.forEach(a1 => {
    arr02.forEach(a2 => {
        newArr.push({
            account: a1.account,
            city: a2.city
        });
    });
});

first of all, there is nothing wrong with your thinking, but you use

cur02.account = cur01.account;
return newArr.push(cur02);

in the above code, you push is cur02 , and js object assignments are passed reference , so the result at the end of the loop is:

// [arr02[0], arr02[1], arr02[2], arr02[0], arr02[1], arr02[2], arr02[0], arr02[1], arr02[2]]

in your last loop, the account value of each object in arr02 becomes "222222222222222" .

so, when you push , you push a new object goes in, instead of a reference to an existing object can solve the problem. In addition, map is changed to forEach ( map and forEach have different usage scenarios).

let newArr = [];
arr01.forEach(cur01 => {
    arr02.forEach(cur02 => {
        newArr.push({
            account: cur01.account,
            city: cur02.city
        });
    })
})