Difference between concat and push?

Question

Why does a return of the push method cause \"Uncaught TypeError: acc.push is not a function\". But a return concat results in the correct solution?

Answer 1

https://dev.to/uilicious/javascript-array-push-is-945x-faster-than-array-concat-1oki Concat is 945x slower than push only because it has to create a new array.