const foo = function* () { yield "a"; yield "b"; yield "c"; }; let str = ""; for (const val of foo()) { str += val; } console.log(str); // Expected output: "abc"
js
function* (param0) { statements } function* (param0, param1) { statements } function* (param0, param1, /* …, */ paramN) { statements } function* name(param0) { statements } function* name(param0, param1) { statements } function* name(param0, param1, /* …, */ paramN) { statements } Note: An
cannot begin with the keyword function to avoid ambiguity with a
. The function keyword only begins an expression when it appears in a context that cannot accept statements.
The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.
The name of a formal parameter for the function. For the parameters' syntax, see the
.
The statements which comprise the body of the function.
A function* expression is very similar to, and has almost the same syntax as, a
. The main difference between a function* expression and a function* declaration is the function name, which can be omitted in function* expressions to create anonymous functions. A function* expression can be used as an
(Immediately Invoked Function Expression) which runs as soon as it is defined, allowing you to create an ad-hoc
. See also the chapter about
for more information.
The following example defines an unnamed generator function and assigns it to x. The function yields the square of its argument:
js
const x = function* (y) { yield y * y; };
Specification
ECMAScript® 2027 Language Specification# sec-generator-function-definitions
guide