규칙 8.19

A function that writes no return type returns what its body does, as TypeScript infers it: a function of the file or of a namespace, a local function (Rule 8.17), each instance of a generic function (Rule 8.9) and of a function that takes a function (Rule 8.18), a method, a getter and a field that holds a function (Rule 8.16) take the type of their first return with a value, the returns after it are typed against that type as against a written one, and one with no such return returns nothing. An arrow function whose body is an expression returns its value, unless the expression is an assignment, ++, -- or a call of a function that returns nothing, which runs as a statement, and the function returns nothing; a method whose every return is return this returns its object, as one written this does (Rule 8.10). A call that needs the type before the body’s turn lowers that body first, so a function may be called above its declaration and from any body. A setter’s value that writes no type takes the type its getter returns, written or said by the getter’s body, as TypeScript types it; an assignment that needs the type before the getter’s body is lowered lowers it first. A call back into a body still being lowered is a call cycle, and must be refused as one (Rule 8.4); so must returns of two types, a bare return beside one with a value, a default parameter value that calls such a function, since every default is lowered before any body, and a setter’s value with no type and no getter, or beside a getter that returns nothing. An entry point writes its return type, which is its output (Rule 8.2). return g() where g returns nothing calls g and returns nothing, in any function.