The following ES6 code's behaviour puzzled a few developers I know.
The results indicated below each snippet are run through
SpiderMonkey's implementation.
It is related to 13.6.3.2. I believe the wording of the current draft
leaves the interaction with closures open to interpretation.
for (let i = 0; i < 3; i++);
console.log(i)
(i is scoped, so it is not defined on line 2. So far so good.)
for (let i = 0; i < 3; i++) {}
console.log(i)
(same)
let funs = [];
for (let i = 0; i < 3; i++) funs[i] = () => console.log(i);
funs[0]()
(shows 3, not 0: i is not captured in the closure)
let funs = [];
for (let i = 0; i < 3; i++) { funs[i] = () => console.log(i); }
funs[0]()
(same)
let funs = [];
for (let i = 0; i < 3; i++) { let j = i; funs[i] = function() {
console.log(j); } }
funs[0]()
(shows 0; i is captured in the closure)
According to me, it would be cleaner if the let binding in any loop
was independently captured in the closure.
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