Binary concatenation

Question

I have following code:

var packet = "\xFF\xFF\xFF\xFF";
packet += "\x6D";
packet += "127.0.0.1:" + this.port;
packet += "\x00";
packet += this.name;
packet += "\x00";
packet += this.state;
packet += "\x00";
packet += "stateA";
packet += "\x00";
packet += "sender";
packet += "\x00";

And I have var id = 32;

I want to get something like this:

...
packet += "\x00";
packet += "sender";
packet += "\x00";
packet += "\x20;

How to convert id number to HEX format and then concatenate it with packet?

I already saw Google, but I haven't found a solution.

Thank you.

[How to convert decimal to hex in javascript](http://stackoverflow.com/a/57805/1053938) — jonhopkins, May 17 '13 at 14:34
possible duplicate of [How to convert decimal to hex in JavaScript?](http://stackoverflow.com/questions/57803/how-to-convert-decimal-to-hex-in-javascript) — TheHippo, May 17 '13 at 14:39
possible duplicate of [JavaScript: create a string or char from an ASCII value](http://stackoverflow.com/questions/602020/javascript-create-a-string-or-char-from-an-ascii-value) — Bergi, May 17 '13 at 14:44
@WasimAbu-Nassar why are you not writing into the buffer directly? Strings are immutable, every time you do `+=` you're destroying and creating a string. Also, (id+"").toString(16) — Benjamin Gruenbaum, May 17 '13 at 14:51

score 4 · Accepted Answer · answered May 17 '13 at 14:34

4

You can use the toString() function of the Number prototype to get the hex representation of your number:

var hex = (23).toString( 16 );

// or

var hex = id.toString( 16 );

EDIT

It seems you just want to add a unicode symbol identified by id. For this use String.fromCharCode()

packet += String.fromCharCode( id );

answered May 17 '13 at 14:34

Sirko

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I've already done this, but: `packet += "\\x" + id.toString(16);` Doesn't work. – user0103 May 17 '13 at 14:34

Bergi · Answer 2 · 2013-05-17T14:42:15.473

2

You can use the String.fromCharCode function:

packet += String.fromCharCode(32); // " "

If you want to get the hex representation, you could use

var hex = (32).toString(16), // "20"
    byte = JSON.parse('"\\u'+('000'+hex).slice(-4)+'"'); // " " == "\u0020"

…but that's ugly :-)

edited May 17 '13 at 14:42

answered May 17 '13 at 14:37

Bergi

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score 1 · Answer 3 · edited May 23 '17 at 12:28

1

You can use String.fromCharCode(23) to do this.

E.G. (in a browser console):

> String.fromCharCode(23) == "\x17"
true

See How to create a string or char from an ASCII value in JavaScript? for more general information.

edited May 23 '17 at 12:28

Community

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answered May 17 '13 at 14:40

intuited

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Binary concatenation

3 Answers3