why new Function() return comments /**/ in arguments?

Question

in chrome 47 and nodejs v0.12

new Function('myArg','return "my function body";')

gives the following results :

function anonymous(myArg /**/) {
  return "my function body"
}

why is there comments /**/ in the function arguments ?

Answer 1

As seen in the following Chromium issue, this is a workaround to remedy an edge case involving unbalanced block comments. As described in the V8 source code:

function NewFunctionString(arguments, function_token) {
  var n = arguments.length;
  var p = '';
  if (n > 1) {
    p = ToString(arguments[0]);
    for (var i = 1; i < n - 1; i++) {
      p += ',' + ToString(arguments[i]);
    }
    // If the formal parameters string include ) - an illegal
    // character - it may make the combined function expression
    // compile. We avoid this problem by checking for this early on.
    if (%_CallFunction(p, ')', StringIndexOfJS) != -1) {
      throw MakeSyntaxError('paren_in_arg_string', []);
    }
    // If the formal parameters include an unbalanced block comment, the
    // function must be rejected. Since JavaScript does not allow nested
    // comments we can include a trailing block comment to catch this.
    p += '\n/' + '**/';
  }
  var body = (n > 0) ? ToString(arguments[n - 1]) : '';
  return '(' + function_token + '(' + p + ') {\n' + body + '\n})';
}