refactor: native Array.flat()

[curbengh]

What does it do?

• Node 12+ feature
  • related Drop Node.js 10 support & Require Node.js >= 12 #4378
• remove misleading "old syntax"
  • "old syntax" implies deprecation,
    but in this case, it's just different syntax
• renews refactor: simplify code #4409 @2997ms
  • This PR uses Array.flat(Infinity) which flattens nesting regardless of depth, otherwise it only flattens one depth.

const arr = [1,2,3,[4,[5,6]]
const flatten = arr.flat()
// [1,2,3,4,[5,6]

const flatten = arr.flat(Infinity)
// [1, 2, 3, 4, 5, 6]

How to test

git clone -b array-flat https://github.com/curbengh/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
  • Existing test case already covered.
• Passed the CI test.
  • Both files still retain 100% coverage.

[coveralls]

Coverage decreased (-0.007%) to 98.119% when pulling e42143f on curbengh:array-flat into ed0f239 on hexojs:master.

[jiangtj]

👍