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'for..in' for null/undefined expression should not be an error in --strictNullChecks #19461
Description
// @strictNullChecks: true
function f(x: { [key: string]: number; } | null | undefined) {
for (const key in x) { // 1
console.log(x[key]); // 2
}
}Expected behavior:
The for..in statement in ECMAScript does not throw if the expression is undefined or null, but rather the loop body is not evaluated. As such, the correct behavior under --strictNullChecks should be:
- The
for..instatement (1) should be legal, even ifxisundefinedornull. - Inside the
for..instatement, thex(2) should no longer be consideredundefinedornull.
Actual behavior:
- The
for..instatement (1) reports the error:Object is possibly 'null' or 'undefined'. - Inside the
for..instatement, thex(2) reports the error:Object is possibly 'null' or 'undefined'.
Activity
[-]'for..in' for 'undefined' expression should not be an error in '--strictNullChecks'[/-][+]'for..in' for undefined expression should not be an error in --strictNullChecks[/+][-]'for..in' for undefined expression should not be an error in --strictNullChecks[/-][+]'for..in' for null/undefined expression should not be an error in --strictNullChecks[/+]