String.Format no funciona en TypeScript

String.Format no funciona enTypeScript.
Error:

The property 'format' does not exist on value of type 
 '{ prototype: String; fromCharCode(...codes: number[]): string; 
 (value?: any): string; new(value?: any): String; }'.
attributes["Title"] = String.format(
    Settings.labelKeyValuePhraseCollection["[WAIT DAYS]"],
    originalAttributes.Days
);

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