Typed `cy.all([...])` command for Cypress consumers

cy-all.ts

// @see https://github.com/cypress-io/cypress/issues/915#issuecomment-475862672
// Modified due to changes to `cy.queue` https://github.com/cypress-io/cypress/pull/17448
// Note: this DOES NOT run Promises in parallel like `Promise.all` due to the nature
// of Cypress promise-like objects and command queue. This only makes it convenient to use the same
// API but runs the commands sequentially.

declare namespace Cypress {
  type ChainableValue<T> = T extends Cypress.Chainable<infer V> ? V : T

  interface cy {
    all<T extends Cypress.Chainable[] | []>(
      commands: T
    ): Cypress.Chainable<{ [P in keyof T]: ChainableValue<T[P]> }>
    queue: any
  }

  interface Chainable {
    chainerId: string
  }
}

const chainStart = Symbol("chainStart")

/**
 * @description Returns a single Chainable that resolves when all of the Chainables pass.
 * @param {Cypress.Chainable[]} commands - List of Cypress.Chainable to resolve.
 * @returns {Cypress.Chainable} Cypress when all Chainables are resolved.
 */
cy.all = function all(commands): Cypress.Chainable {
  const _ = Cypress._
  // eslint-disable-next-line
  const chain = cy.wrap(null, { log: false })
  const stopCommand = _.find(cy.queue.get(), {
    attributes: { chainerId: chain.chainerId },
  })
  const startCommand = _.find(cy.queue.get(), {
    attributes: { chainerId: commands[0].chainerId },
  })
  const p = chain.then(() => {
    return cy.wrap(
      // @see https://lodash.com/docs/4.17.15#lodash
      _(commands)
        .map(cmd => {
          return cmd[chainStart]
            ? cmd[chainStart].attributes
            : _.find(cy.queue.get(), {
                attributes: { chainerId: cmd.chainerId },
              }).attributes
        })
        .concat(stopCommand.attributes)
        .slice(1)
        .flatMap(cmd => {
          return cmd.prev.get("subject")
        })
        .value()
    )
  })
  p[chainStart] = startCommand
  return p
}