Javascript ascii string to hex byte array

Question

I am trying to convert an ASCII string into a byte array.

Problem is my code is converting from ASCII to a string array and not a Byte array:

var tx = '[86400:?]';
for (a = 0; a < tx.length; a = a + 1) {
 hex.push('0x'+tx.charCodeAt(a).toString(16));
}

This results in:

 [ '0x5b','0x38','0x36','0x30','0x30','0x30','0x3a','0x3f','0x5d' ]

But what I am looking for is:

[0x5b,0x38 ,0x30 ,0x30 ,0x30 ,0x30 ,0x3a ,0x3f,0x5d]

How can I convert to a byte rather than a byte string ?

This array is being streamed to a USB device:

device.write([0x5b,0x38 ,0x30 ,0x30 ,0x30 ,0x30 ,0x3a ,0x3f,0x5d])

And it has to be sent as one array and not looping sending device.write() for each value in the array.

• h2ooooooo: 0x5b isn't actually 0x5b, but rather it's just a simple int with the value 91. Save these as an int (tx.charCodeAt(a)) instead, and everything will be fine.
• Osiris: Numbers are numbers, and they're always stored in binary. If you want the hex representation, store it as a string (as you are now), or use hex.push(tx.charCodeAt(a));, which will store the ASCII codes, and use .toString(16) to convert to hex while printing.
• Mike Edward Moras: possible duplicate of JavaScript Converting string values to hex

Answer 1

A single liner :

 '[86400:?]'.split ('').map (function (c) { return c.charCodeAt (0); })

returns

 [91, 56, 54, 52, 48, 48, 58, 63, 93]

This is, of course, is an array of numbers, not strictly a "byte array". Did you really mean a "byte array"?

Split the string into individual characters then map each character to its numeric code.

Per your added information about device.write I found this :

Writing to a device

Writing to a device is performed using the write call in a device handle. All writing is synchronous.

device.write([0x00, 0x01, 0x01, 0x05, 0xff, 0xff]);

on https://npmjs.org/package/node-hid

Assuming this is what you are using then my array above would work perfectly well :

device.write('[86400:?]'.split ('').map (function (c) { return c.charCodeAt (0); }));

As has been noted the 0x notation is just that, a notation. Whether you specify 0x0a or 10 or 012 (in octal) the value is the same.

• crankshaft: Thanks, yes it has to be a Hex byte array as the output is streamed to a usb device: device.write([0x5b,0x38 ,0x30 ,0x30 ,0x30 ,0x30 ,0x3a ,0x3f,0x5d]). So I really need a way of creating a hex-byte array !
• Alnitak: a "byte array" is not "hex", it is often merely presented in hex.
• HBP: What environment are you running? node.js ?
• crankshaft: Excellent, thanks, yes it is node.js and your googling was correct this is using node-hid. After some more testing, I now understand that it's not necessary to send the array in hex format so your solution works. Thanks again.

Answer 2

 function getBytes(str){
 let intArray=str.split ('').map (function (c) { return c.charCodeAt (0); });
 let byteArray=new Uint8Array(intArray.length);
 for (let i=0;i<intArray.length;i++)
 byteArray[i]=intArray[i];
 return byteArray;
 }
 device.write(getBytes('[86400:?]'));