add ascii encoding conversion

index.d.ts

@@ -249,3 +249,16 @@ console.log(hexToUint8Array('48656c6c6f'));
 ```
 */
 export function hexToUint8Array(hexString: string): Uint8Array;
+
+/**
+Convert a string to a `Uint8Array` using ASCII encoding.
+
+@example
+```
+import { asciiStringToUint8Array } from 'uint8array-extras';
+
+console.log(asciiStringToUint8Array('Hello'));
+//=> Uint8Array [72, 101, 108, 108, 111]
+```
+*/
+export function asciiStringToUint8Array(string: string): Uint8Array;

index.js

@@ -220,3 +220,19 @@
 
 	return bytes;
 }
+
+export function asciiStringToUint8Array(string) {
+	assertString(string);
+
+	const bytes = new Uint8Array(string.length);
+
+	for (let i = 0; i < string.length; i++) {
+		const code = string.charCodeAt(i);
+		if (code > 127) {
+			throw new Error(`Non-ASCII character detected at position ${i}`);
+		}
+		bytes[i] = code;
+	}
+
+	return bytes;
+}