Run results for: flatMap count vs reduce count

Run details:

User agent: Mozilla/5.0 (iPad; CPU OS 14_8 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/96.0.4664.53 Mobile/15E148 Safari/604.1

Browser: Chrome Mobile iOS 96

Operating system: iOS 14.8

Device Platform: Tablet

Date tested: 2 years ago

Test name	Executions per second
reduce with concat	8880006.0 Ops/sec
flatMap	2469771.0 Ops/sec

Script Preparation code:

var arr = [
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
  {
    loanId: 1077579,
    missingDocs: [
      { docTypeID: 4, docType: "CEMA" },
      { docTypeID: 14, docType: "Policy" },
    ],
  },
];

Tests:

reduce with concat
arr.reduce((acc, loan) => acc + loan.missingDocs.length, 0)
flatMap
arr.flatMap(loan => loan.missingDocs).length

Run results for: flatMap count vs reduce count

reduce with concat

flatMap