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Improve typeof x === "function" narrowing for non-unions

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This commit is contained in:
Anders Hejlsberg
2018-06-02 17:42:07 -07:00
parent ed728f186b
commit 0ff597c3a8
1 changed files with 4 additions and 1 deletions
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5
src/compiler/checker.ts
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@@ -14112,11 +14112,14 @@ namespace ts {
if (operator === SyntaxKind.ExclamationEqualsToken || operator === SyntaxKind.ExclamationEqualsEqualsToken) {
assumeTrue = !assumeTrue;
}
if (type.flags & TypeFlags.Any && literal.text === "function") {
return type;
}
if (assumeTrue && !(type.flags & TypeFlags.Union)) {
// We narrow a non-union type to an exact primitive type if the non-union type
// is a supertype of that primitive type. For example, type 'any' can be narrowed
// to one of the primitive types.
const targetType = typeofTypesByName.get(literal.text);
const targetType = literal.text === "function" ? globalFunctionType : typeofTypesByName.get(literal.text);
if (targetType) {
if (isTypeSubtypeOf(targetType, type)) {
return targetType;