How to honor escape sequences the way String() does

Question

I have a string that contains backslashed escape sequences, such as:

AB\0C\xff

Is there a simple way to parse that that interprets backslashed escape sequences using the same rules as JavaScript string parsing such that the above would generate the byte sequence:

0x41 0x42 0x00 0x43 0xff

?

I tried String(line) but of course that had no effect.

FWIW, here's a short node.js program to demonstrate what I'm after:

'use strict'

const readline = require('readline');

var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: false
});

rl.on('line', function(line) {
  processLine(line);
});

function hexify(line) {
  function hex(v) {
    return ((v < 16) ? '0' : '') + v.toString(16);
  };
  var s=[];
  for (var i=0; i<line.length; i++) {
    s.push(hex(line.charCodeAt(i)));
  };
  return s.join(' ');
}

function honorEscapes(line) {
  return String(line);          // this doesn't do what I want
};

function processLine(line) {
  console.log('raw    ' + hexify(line));
  console.log('parsed ' + hexify(honorEscapes(line)));
};

Running it:

$ node escape.js
AB\0\C\xff
raw    41 42 5c 30 5c 43 5c 78 66 66
parsed 41 42 5c 30 5c 43 5c 78 66 66

Answer 1

You might be looking for JSON.parse , which parses JSON strings including escaped characters.

Of course that does not encompass all the weird escapes in JavaScript string literals . Depending on which of those you do need, add them manually for example using regex:

.replace(/\\0/g, '\u0000')
.replace(/\\x([0-9a-fA-F]{2})/g, function(m, c) { return String.fromCharCode(parseInt(c, 16)); }