Is this valid or invalid ES6?

valid-or-invalid.es6

function * append (...iterables) {
  for (const iterable of iterables) {
    yield * iterable;
  }
}

const lyrics = append(["a", "b", "c"], ["one", "two", "three"], ["do", "re", "me"]);

for (const word of lyrics) {
  console.log(word);
}
  //=>
    a
    b
    c
    one
    two
    three
    do
    re
    me

Works on ES6 Fiddle, but not on Babel’s online REPL.

Is this valid or invalid code?

Seems to be functioning in Babel's online REPL on my machine:

Seems to work for me on Babel's REPL: https://babeljs.io/repl/#?evaluate=true&presets=es2015&code=function%20*%20append%20(...iterables)%20%7B%0A%20%20for%20(const%20iterable%20of%20iterables)%20%7B%0A%20%20%20%20yield%20*%20iterable%3B%0A%20%20%7D%0A%7D%0A%0Aconst%20lyrics%20%3D%20append(%5B%22a%22%2C%20%22b%22%2C%20%22c%22%5D%2C%20%5B%22one%22%2C%20%22two%22%2C%20%22three%22%5D%2C%20%5B%22do%22%2C%20%22re%22%2C%20%22me%22%5D)%3B%0A%0Afor%20(const%20word%20of%20lyrics)%20%7B%0A%20%20console.log(word)%3B%0A%7D

Side note: not sure we can use const in a loop, this is node 5.3.0 on my system:

@bignimbus
V8 seems to ignore reassignment to constants in a loop, while Firefox does not: 'SyntaxError: invalid for/in left-hand side'

@raganwald
except for consts it seems to work, why shouldn't it?
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/yield*

@raganwald, I agree with @nikitadyumin, the only issue here is const. Runs fine on Edge (with full generator support) when const becomes let.