1 files changed, 39 insertions, 0 deletions
diff --git a/cli/js/lib.deno.unstable.d.ts b/cli/js/lib.deno.unstable.d.ts
index 0a80eb2c6..dd8de2eb6 100644
--- a/cli/js/lib.deno.unstable.d.ts
+++ b/cli/js/lib.deno.unstable.d.ts
@@ -1248,4 +1248,43 @@ declare namespace Deno {
 
   /** **UNSTABLE**: The URL of the file that was originally executed from the command-line. */
   export const mainModule: string;
+
+  /** Synchronously truncates or extends the specified file stream, to reach the
+   * specified `len`.  If `len` is not specified then the entire file contents
+   * are truncated.
+   *
+   * ```ts
+   * // truncate the entire file
+   * const file = Deno.open("my_file.txt", { read: true, write: true, truncate: true, create: true });
+   * Deno.ftruncateSync(file.rid);
+   *
+   * // truncate part of the file
+   * const file = Deno.open("my_file.txt", { read: true, write: true, create: true });
+   * Deno.write(file.rid, new TextEncoder().encode("Hello World"));
+   * Deno.ftruncateSync(file.rid, 7);
+   * const data = new Uint8Array(32);
+   * Deno.readSync(file.rid, data);
+   * console.log(new TextDecoder().decode(data)); // Hello W
+   * ```
+   */
+  export function ftruncateSync(rid: number, len?: number): void;
+
+  /** Truncates or extends the specified file stream, to reach the specified `len`. If
+   * `len` is not specified then the entire file contents are truncated.
+   *
+   * ```ts
+   * // truncate the entire file
+   * const file = Deno.open("my_file.txt", { read: true, write: true, create: true });
+   * await Deno.ftruncate(file.rid);
+   *
+   * // truncate part of the file
+   * const file = Deno.open("my_file.txt", { read: true, write: true, create: true });
+   * await Deno.write(file.rid, new TextEncoder().encode("Hello World"));
+   * await Deno.ftruncate(file.rid, 7);
+   * const data = new Uint8Array(32);
+   * await Deno.read(file.rid, data);
+   * console.log(new TextDecoder().decode(data)); // Hello W
+   * ```
+   */
+  export function ftruncate(rid: number, len?: number): Promise<void>;
 }