Type guard not working in returned function

[andraaspar]

TypeScript Version: 2.2.0-dev.20161202

Code

function getGetter() {
	let data = {}
	data['bar'] = 1
	
	if (hasBar(data)) {
		return () => data.bar // Property 'bar' does not exist on type '{}'.
	}
}

function hasBar(thing): thing is {bar: number} {
	return typeof thing.bar == 'number'
}

Expected behavior:
Compile successfully.

Actual behavior:

index.ts(6,21): error TS2339: Property 'bar' does not exist on type '{}'.

[ahejlsberg]

Your example works if you use const to declare data. Type guards for let variables are not in effect in nested functions because the variable might be reassigned. See #8849.

[andraaspar]

I see. You are right.