如何“重新启用” JavaScript中的特殊字符序列？

Question

If I have a defined String variable as (eg) :

 var testString="not\\n new line";

it's value of course will be not\\n new line .

But if use directly "not\\n new line" the test string will contain new line.

So what is the easiest way to turn the testString to a string that contains a new line and all other special character sequences that are "disabled" with double backslashes? Using replaces? It look like it will take a lot of time if it used for unicode characters sequnces.

Answer 1

JSON.parse('"' + testString + '"')

will parse JSON and interpret JSON escape sequences which covers all JS escape sequences except \\x hex, \\v , and the non-standard octal ones.

People will tell you to eval it. Don't. eval is hugely overpowered for this, and that extra power comes with the risk of XSS vulnerabilities.

var jsEscapes = {
  'n': '\n',
  'r': '\r',
  't': '\t',
  'f': '\f',
  'v': '\v',
  'b': '\b'
};

function decodeJsEscape(_, hex0, hex1, octal, other) {
  var hex = hex0 || hex1;
  if (hex) { return String.fromCharCode(parseInt(hex, 16)); }
  if (octal) { return String.fromCharCode(parseInt(octal, 8)); }
  return jsEscapes[other] || other;
}

function decodeJsString(s) {
  return s.replace(
      // Matches an escape sequence with UTF-16 in group 1, single byte hex in group 2,
      // octal in group 3, and arbitrary other single-character escapes in group 4.
      /\\(?:u([0-9A-Fa-f]{4})|x([0-9A-Fa-f]{2})|([0-3][0-7]{0,2}|[4-7][0-7]?)|(.))/g,
      decodeJsEscape);
}

Answer 2

If you want to express a string so that Javascript could interpret it (the equivalent of Python's repr function), use JSON.stringify :

var testString="not\n new line";
console.log(JSON.stringify(testString))

will result in "not\\n new line" (quotes and all).