isIdentifierChar = function(code) {
    if (code < 48) return code === 36;
    if (code < 58) return true;
    if (code < 65) return false;
    if (code < 91) return true;
    if (code < 97) return code === 95;
    if (code < 123) return true;
    return code >= 0xaa && nonASCIIidentifier.test(String.fromCharCode(code));
  }
Test whether a given character is part of an identifier.

@param {number} code
@returns {boolean}