"HeadlessChrome" in User-Agent forces downgrade to es2015

[mootari]

Whenever the User-Agent header contains "HeadlessChrome", the build target "es2015" will be selected, regardless of the specified version:

$ curl -s -H "User-Agent: HeadlessChrome/80" https://esm.sh/react@18.2.0
/* esm.sh - react@18.2.0 */
export * from "https://esm.sh/stable/react@18.2.0/es2015/react.js";
export { default } from "https://esm.sh/stable/react@18.2.0/es2015/react.js";

$ curl -s -H "User-Agent: HeadlessChrome/109" https://esm.sh/react@18.2.0
/* esm.sh - react@18.2.0 */
export * from "https://esm.sh/stable/react@18.2.0/es2015/react.js";
export { default } from "https://esm.sh/stable/react@18.2.0/es2015/react.js";

$ curl -s -H "User-Agent: Chrome/80" https://esm.sh/react@18.2.0
/* esm.sh - react@18.2.0 */
export * from "https://esm.sh/stable/react@18.2.0/es2021/react.js";
export { default } from "https://esm.sh/stable/react@18.2.0/es2021/react.js";

$ curl -s -H "User-Agent: Chrome/109" https://esm.sh/react@18.2.0
/* esm.sh - react@18.2.0 */
export * from "https://esm.sh/stable/react@18.2.0/es2022/react.js";
export { default } from "https://esm.sh/stable/react@18.2.0/es2022/react.js";

$ curl -s -H "User-Agent: HeadlessSomething/109" https://esm.sh/react@18.2.0
/* esm.sh - react@18.2.0 */
export * from "https://esm.sh/stable/react@18.2.0/esnext/react.js";
export { default } from "https://esm.sh/stable/react@18.2.0/esnext/react.js";

Please note that react is an arbitrary example. The issue was first encountered with @observablehq/stdlib, where the target causes the build to fail:

$ curl -s -H "User-Agent: HeadlessChrome/109" https://esm.sh/@observablehq/stdlib@5.3.2
/* esm.sh - error */
throw new Error("[esm.sh] " + "esbuild: Transforming async generator functions to the configured target environment (\"es2015\") is not supported yet");
export default null;

[ije]

fixed, thanks

[mootari]

Thank you!