You basically want to group something. For grouping you can usually use .reduce()

On every iteration you iterate over your object entries with Object.entries() and then you always check if your previous value already has that key, if yes, you push it, if not, you create a new array and put your value inside of it.

let myArray = [{a:1,b:1,c:1,d:1},{a:2,b:2,c:2,d:2},{a:3,b:3,c:3,d:3},{a:4,b:4,c:4,d:4}]


let result = myArray.reduce((prev, curr) => {
   Object.entries(curr).forEach(([key, value]) => {
      if(prev[key]) {
         prev[key].push(value)
      } else {
         prev[key] = [value]
      }
   })
   return prev;
}, {})


console.log(result);

Alternatively you can also do it in a for loop, in case you are unfamiliar with the reduce method.

const myArray = [{a:1,b:1,c:1,d:1},{a:2,b:2,c:2,d:2},{a:3,b:3,c:3,d:3},{a:4,b:4,c:4,d:4}]

const wantedProperties = ['a', 'b', 'd']

const mydict = {}
for (const item of myArray) {
  for (const [key, value] of Object.entries(item)) {
    if (wantedProperties.includes(key)) {
     mydict[key] = (mydict[key] || []).concat(value)
    }
  }
}

console.log(mydict)

let targetArray = [{a:1,b:1,c:1,d:1},{a:2,b:2,c:2,d:2},{a:3,b:3,c:3,d:3},{a:4,b:4,c:4,d:4}]


let result = targetArray.reduce((accc, curr) => {
   Object.entries(curr).forEach(([key, value]) => {
      if(!accc[key]) {
         accc[key] = [value]
      } else {
         accc[key].push(value)
      }
   })
   return accc;
}, {})


console.log(result);