Question

i was digging throug some code (async module for nodejs) and ran into the following notation:

return fn.apply(null, [async.forEachSeries].concat(args));

if seen this notation using the square brackets alot, but have no idea whoat it means exactly.
is this related to ES5?

greetings!

Answer 1

It’s really quite simple. You are basically gluing two arrays together and passing the resulting array as second argument to apply. See:

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/concat

e.g.:

// this should clarify
console.log([1, 2, 3].concat([4, 5]));