Why doesn't this snippet work in the node repl?

Question

I just started playing with ES6 and Node, experimenting with the new features in a node repl:

{
  const str = 'Alice';
  let arr = [];

  for (let c of str) {
    arr.push(c);
  }

  arr;
}

Errors thrown:

const str = 'Alice';
      ^^^
SyntaxError: Unexpected identifier

  arr;
ReferenceError: arr is not defined

I couldn't figure out what I did wrong (thinking maybe the block statement doesn't work that way), so I turned to the Chrome console to confirm. The snippet works fine. So why it doesn't work in the node repl (v7.8.0)?

Answer 1

Eh, the problem is how you have defined your code in {...} . It should work as expected, as you have said that it works in chrome's dev console. ( note, what you did is somewhat unusual use of the destructuring assignment but ... it's a nice thing to know why it doesn't work in repl! )

Apparently repl stops creating when you're using the ending curly brace, the } , thus executing the content defined within { and } . Let add your code step by step in repl and you will get an error when you add the } of your for-loop:

> {
... const str = 'Alice';
... let arr = [];
... for (let c of str) {
..... arr.push(c);
..... }
const str = 'Alice';
      ^^^
SyntaxError: Unexpected identifier

So the code that the parser receives is

{
  const str = 'Alice';
  let arr = [];

  for (let c of str) {
    arr.push(c);
  }

Which is of course not correct. If you re-write the code a bit, without having an ending } in the scope, then it works! Try this code

{
  const str = 'Alice';
  let arr = [];
  for (let c of str) arr.push(c);
  arr;
}

image:

This works. The problem may lie at how node repl treats the {} stuff.

UPDATE

I was intrigued, so checked this further. The problem is that repl starts to evaluate your statement once you have pressed after placing a } character. I have checked this and if you do the following:

{
    const a = 'Alice';
    let arr = [];
    for (let c of a) {
        arr.push(c);
    } arr; }

Please note the use of two } in one line. You will get an answer;

> {
...     const a = 'Alice';
...     let arr = [];
...     for (let c of a) {
.....         arr.push(c);
.....     } arr; }
[ 'A', 'l', 'i', 'c', 'e' ]

Congratulations. You have discovered a bug in node repl.