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Error with let: "Identifier '*' has already been declared" on REPL #8441
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I guess we may be able to provide a better error message? Maybe?
@Fishrock123 how would you improve the error message? To me it appears pretty clear. The only thing that is really confusing is that you get two different errors depending on how you try and redefine the variable. E.g.
> let broken = foo ReferenceError: foo is not defined > let broken = 'foo' TypeError: Identifier 'broken' has already been declared > broken = 'foo'; ReferenceError: broken is not definedProviding better error messages would mean catching all Reference errors, and comparing the error messages to these known values, then changing the message. This seems like a lot of work for something that is spec compliant.
Any objections to closing this issue since it's a wontfix?
Let's close, I don't think we'll fix this anytime soon.
#8309 (comment) makes an interesting suggestion of turning uninitialized bindings into undefined values but that probably needs support in V8.
@bnoordhuis We can preprocess it before passing to
vm. I'll give PR if it seems good to you.function preprocess(code) { ... const letBinding = /^\s*let\s+([^\s=]+)\s*(?==)/; const letMatch = cmd.match(letBinding); if (letMatch && letMatch[0] !== letMatch.input) { const binding = letMatch[1]; cmd = cmd.replace(letMatch[0], `let ${binding};\n${binding}`); } ... }
node 🙈 ₹ git:(upstream ⚡ repl.let) ./node > let x = foo ReferenceError: foo is not defined at repl:2:4 at sigintHandlersWrap (vm.js:22:35) at sigintHandlersWrap (vm.js:96:12) at ContextifyScript.Script.runInThisContext (vm.js:21:12) at REPLServer.defaultEval (repl.js:313:29) at bound (domain.js:280:14) at REPLServer.runBound [as eval] (domain.js:293:12) at REPLServer.<anonymous> (repl.js:513:10) at emitOne (events.js:101:20) at REPLServer.emit (events.js:188:7) > x undefined > x = 3 3 >
A bit too much of a hack, IMO. I know perfect is the enemy of good but it would fail on simple inputs like
let x = 1, y = boom,let /* comment */ y = boom,f(); let y = boom, etc.Reacted by Prince John Wesley and Katy PetrovaI used
let, but the variable can't be reassigned. It's maybe a bug of node@6.9.1 REPLThis is very weird behaviour as i cannot use that variable and can lead to memory leak as memory is already given to this obj but the compiler can not clean it.
class Drone {
constructor(id, name) {
this.id = id;
this.name = name;
}
}let drone = new Drone(A1223, flyer);
console.log('drone :' + drone.id +' ' + drone.name);
I keep getting this error "VM55:1 Uncaught SyntaxError: Identifier 'Drone' has already been declared
at :1:1" please can someone tell me why?@DinmaOtutu How is this related to node REPL? REPL doesn't produce errors with "VMxx" in the message. Looks like an error in a browser, not in node...
Also, I guess you already declared it further above or in a previous statement. That's what the error literally tells you.
class Drone {
constructor(id, name) {
this.id = id;
this.name = name;
}
}let drone = new Drone(A1223, flyer);
console.log('drone :' + drone.id +' ' + drone.name);
I keep getting this error "VM55:1 Uncaught SyntaxError: Identifier 'Drone' has already been declared
at :1:1" please can someone tell me why?I'm running into the same problem in some of my code. I don't understand why it has said that Drone has already been declared when it wasn't declared as a variable. It was set as a class. Are setting a class and setting a variable both declarations?
Yes,
class X {}is almost the same asconst X = class {}. But this has nothing to do with this REPL-specific issue.
The problem I'm seeing is that if during declaring a variable with
letsomething throws - that identifier is "taken", but I can't use it.Essentially like this (stripped unnecessary stack).
I'm seeing this for a long time, but never took an effort to look into it more.
Now I'm curious - is this expected behaviour? Why? If not, how can one go about and fix it?
It's on Node 5 and latest 6, but I believe I've seen it on older versions as well.