non-strict direct eval in top level scope

Francisco Tolmasky tolmasky at
Thu Jan 22 17:03:19 PST 2015

Apologies as I believe this has been discussed before ( ), but just
trying to get some clarification as to the current state of things, and
have not been able to find this information (in a format I can understand).
Namely, I’m curious whether eval(“let x = 5”) adds x to the current scope,
if not in strict mode, at the “top level” (i.e. not in a function) and
called directly. My impression was that with let it should not be adding
anything to the current scope, but my tests in Mozilla Firefox (in the
console) seem to suggest they do:

> eval(“let x = 5”)
> undefined
> x
> 5

In fact, even in functions:

> (function() { eval("let xyz = 555"); console.log(xyz) })()
> 555

In if statements, it seems to be tacked onto the global scope:

> if (true) { eval(“let x = 5”) } x
> 5

If these are just bugs that’s fine, but if not, could someone tell me the
expected behavior? Is it always supposed to act as if its creating a new
scope for the blocks, or always *except* for top level evals? Or never?



Francisco Tolmasky
tolmasky at
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