You can't do this, but you can instead do something like: function saveItem(andClose) { if(andClose === undefined) { andClose = false; } }. ... <看更多>

function decode(base64url: string, encoding: string = "utf8"): string { return Buffer.from(toBase64(base64url), "base64"). ... <看更多>

All optional parameters for concrete functions must have default values, even if that value is undefined . In contrast to concrete functions ... ... <看更多>

You are setting the default value of the method parameter to the default value of a boolean (i.e. false ). If you change either of these notions ... ... <看更多>