Just use the native method map (read more here or here) like this:

const array= [
  { "test": 1},
  { "test": 2},
  { "test": 3},
  { "test": 4},
];
const newArray = array.map(p => p.test);
console.log(JSON.stringify(newArray)); //[1,2,3,4]

Hope this helps.. ;D

You can use the map function for this https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map :

const newarray = array.map(x => x.test);
console.log(newarray);

const result = {};

yourArray.forEach( ( object ) => {
  const keys = Object.keys( object );
  for ( let i = 0; i < keys.length; i++ ) {
     const key = keys[ i ];
     if ( ! key in result ) { 
        result[ key ] = [];
     }
     result[key] = [...result[key], ...object[key] ];
  }
});

console.log( result );

In this case:

1. You need to iterate in your array
2. On each iteration you have a new object
3. From there you iterate in all the keys of that current object
4. If the key does not exists in your result create a new empty array
5. Merge the value from the result with the current value of the object.
6. Values are stored in result.