Is the keyword "let" trustworthy in JS?

Asked Jun 22 '16 at 08:53

Active Jun 22 '16 at 08:58

Viewed 61 times

I've never really used let in JS yet. But with a few dev in my company we just found out something quite strange. I can't explain it.

When I execute the following code in a browser (tested on Chrome Version 51.0.2704.63 (64-bit))

for (let i = 0; i<10000; i++) {
    console.log(typeof null == 'undefined')
} 

4917 false
5083 true

If I use var instead of let then I get 10000 false, which is what's expected.

I tried to run it several times on several webpages and the result is always the same. It makes me wonder if let is correctly integrated within the browsers, because this doesn't seem trustworthy at all and I wonder what kind of other bugs this can produce.

Any insight? The fact that the result is always the same seems to indicate that there is some logic behind it, but I can't grasp it.

edited Jun 22 '16 at 08:58

asked Jun 22 '16 at 08:53

Vadorequest

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It was discussed here http://stackoverflow.com/questions/37939455/why-does-the-value-of-typeof-null-change-inside-a-loop – k102 Jun 22 '16 at 08:56
Works fine for me (`52.0.2743.41 beta-m (64-bit)`) – toster-cx Jun 22 '16 at 08:56
3

This has nothing to do with `let`. Yes, it's just a simple bug going viral. – Bergi Jun 22 '16 at 08:57
Very interesting, for me it is `4099 false` and `5901 true` on Chrome . Then FireFox `4917 false` and `5083 true`... – Linh Pham Jun 22 '16 at 08:58
1

I assumed it was related to `let` since the result was correct using `var`. – Vadorequest Jun 22 '16 at 08:58

Is the keyword "let" trustworthy in JS?

0 Answers0