first "let a = 1;" result: wasThrown = false
second "let a = 1;" result: wasThrown = true
exception message: Uncaught SyntaxError: Identifier 'a' has already been declared
    at <anonymous>:1:1
{"result":{"type":"number","value":42,"description":"42"}}
function dir(value) { [Command Line API] }
function dirxml(value) { [Command Line API] }
function keys(object) { [Command Line API] }
function values(object) { [Command Line API] }
function profile(title) { [Command Line API] }
function profileEnd(title) { [Command Line API] }
function inspect(object) { [Command Line API] }
function copy(value) { [Command Line API] }
function clear() { [Command Line API] }
function debug(function) { [Command Line API] }
function undebug(function) { [Command Line API] }
function monitor(function) { [Command Line API] }
function unmonitor(function) { [Command Line API] }
function table(data, [columns]) { [Command Line API] }