ArrowFunctionExpression's scope is always strict scope

[futpib]

It seems to be deliberate that eslint-scope always sets isStrict to true for arrow function scopes. But this is not how it works in all the engines I could get my hands to.

I used assignment to an undeclared variable to check if the code is in strict mode:

With explicit strict mode, we get an error:

node -e '"use strict"; (() => { a = 5 })()'
# ReferenceError: a is not defined

Without "use strict" an error is not thrown, which means it's not in strict mode, but eslint-scope would treat the scope as strict anyway:

node -e '(() => { x = 1 })()'

I also checked with the spec's definition of strict mode code, and it seems that arrow functions should not get any special treatment (only classes should): https://www.ecma-international.org/ecma-262/#sec-strict-mode-code

eslint-scope/lib/scope.js

Lines 52 to 55 in 3e69fdc

	// ArrowFunctionExpression's scope is always strict scope.
	if (block.type === Syntax.ArrowFunctionExpression) {
	return true;
	}

eslint-scope/tests/es6-arrow-function-expression.js

Line 55 in 3e69fdc

expect(scope.isStrict).to.be.true;

[mysticatea]

Thank you for the report!

Sounds like a bug.
Are you willing to submit a pull request?

[not-an-aardvark]

Reopening because the fix was reverted (see #51)