JS has no ASCII strings, they're intrinsically UTF-16.
In a browser you're out of luck. If you're coding for node.js you're lucky!
You can use a buffer to transcode strings into octets and then manipulate the binary data at will. But you won't get necessarily a valid string back out of the buffer once you've messed with it.
Either way you'll have to read more about it here:
https://mathiasbynens.be/notes/javascript-encoding
or here:
https://nodejs.org/api/buffer.html
EDIT: in the comment you say you use node.js, so this is an excerpt from the second link above.
const buf5 = Buffer.from('test');
// Creates a Buffer containing ASCII bytes [74, 65, 73, 74].
To create the SOH character embedded in a common ASCII string use the common escape sequence\x01 like so:
const bufferWithSOH = Buffer.from("string with \x01 SOH", "ascii");
This should do it. You can then send the bufferWithSOH content to an output stream such as a network, console or file stream.
Node.js documentation will guide you on how to use strings in a Buffer pretty well, just look up the second link above.