When I use a for in statement, js2 mode doesn't recognize the new variable:

let foo = {bar: 1};

for(key in foo) {

It prints: Undeclared variable or function 'key'


It warns you that the key variable is undeclared, and using it like this, you leak it into the global namespace.

Try this is your browser console:

> let foo = {bar: 1};

> for(key in foo) {}

> key
=> "bar"

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