Move array elements to start of array

move-elements-to-start.spec.ts

import { moveElementsToStart } from '../move-elements-to-start'

describe('moveElementsToStart', () => {
  it('should move simple elements to start', () => {
    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], [])).toEqual([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['AU', 'RO'])).toEqual([
      'AU', 'RO', 'CH', 'IT', 'RU', 'MD', 'US'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['RO', 'AU'])).toEqual([
      'RO', 'AU', 'CH', 'IT', 'RU', 'MD', 'US'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['CH', 'IT'])).toEqual([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['US', 'RO'])).toEqual([
      'US', 'RO', 'CH', 'IT', 'RU', 'MD', 'AU'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], [], i => i)).toEqual([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['AU', 'RO'], i => i)).toEqual([
      'AU', 'RO', 'CH', 'IT', 'RU', 'MD', 'US'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['CH', 'IT'], i => i)).toEqual([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ])

    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['US', 'RO'], i => i)).toEqual([
      'US', 'RO', 'CH', 'IT', 'RU', 'MD', 'AU'
    ])
  })

  it('should move complex elements to start', () => {
    expect(moveElementsToStart([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' }, { code: 'US' }, { code: 'RO' },
    ], [], i => i.code)).toEqual([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' }, { code: 'US' }, { code: 'RO' },
    ])

    expect(moveElementsToStart([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' }, { code: 'US' }, { code: 'RO' },
    ], ['AU', 'RO'], i => i.code)).toEqual([
      { code: 'AU' }, { code: 'RO' }, { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'US' },
    ])

    expect(moveElementsToStart([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' }, { code: 'US' }, { code: 'RO' },
    ], ['RO', 'AU'], i => i.code)).toEqual([
      { code: 'RO' }, { code: 'AU' }, { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'US' },
    ])

    expect(moveElementsToStart([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' }, { code: 'US' }, { code: 'RO' },
    ], ['CH', 'IT'], i => i.code)).toEqual([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' }, { code: 'US' }, { code: 'RO' },
    ])

    expect(moveElementsToStart([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' }, { code: 'US' }, { code: 'RO' },
    ], ['US', 'RO'], i => i.code)).toEqual([
      { code: 'US' }, { code: 'RO' }, { code: 'CH' }, { code: 'IT' }, { code: 'RU' }, { code: 'MD' }, { code: 'AU' },
    ])
  })

  it('should do nothing if id not found', () => {
    expect(moveElementsToStart([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ], ['USA'])).toEqual([
      'CH', 'IT', 'RU', 'MD', 'AU', 'US', 'RO'
    ])
  })

  it('should do nothing if complex object and not getId arg', () => {
    expect(moveElementsToStart([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' },
    ], ['RU'])).toEqual([
      { code: 'CH' }, { code: 'IT' }, { code: 'RU' },
    ])
  })
})

move-elements-to-start.ts

export function moveElementsToStart<T = any>(items: T[], ids: unknown[], getId: (item: T) => unknown = item => item): T[] {
  items = items.slice()
  const extractedItems = ids
    .map(id => items.find(item => getId(item) === id))
    .filter((item): item is T => item !== undefined)
    .map(item => items.splice(items.indexOf(item), 1)[0])

  return [...extractedItems, ...items]
}