a quick function to merge two arrays of objects where a child from one array share a value (like an ID) with a single child of the other array

mergedById.ts

// note: to use this function, replace '.id' in line 4 
// with the property youre using to match children

const mergeById = (a1: Array<object>, a2: Array<object>) =>
  a1.map(itm: object | null => ({
    ...a2.find(e: object | null => (e.id === itm.id)),
    ...itm
}))