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I am using ES6 with Babel in my project and I am getting an error when I declare one of my const

'use strict';

const APP = window.APP = window.APP || {};
const _ = window._;

APP.personalCard = (function () {

   ...

}());

the error

Uncaught TypeError: Identifier 'APP' has already been declared

and that is the whole file, I don't have that declare anywhere else in that file. But I have declared that var in the top of the other files.

What do you think it should be ?

But I have declared that var in the top of the other files.

That's the problem. After all, this makes multiple declarations for the same name in the same (global) scope - which will throw an error with const.

Instead, use var, use only one declaration in your main file, or only assign to window.APP exclusively. Or use ES6 modules right away, and let your module bundler/loader deal with exposing them as expected.

In order to stop getting the error, I have to close the browser tab that the dev tools Get error Identifier 'sum' has already been declared I'm working on online tutorials for learning, and I'm realizing there's tons of learn X for javascript videos. FunctionDeclaration B is registered only in the scope where the function is declared. So what happens here is the class's own scope can run the mangler as it doesn't come under evalScope/unsafeScope. And it tries to rename to the same name. Not sure whether this is a bug in babel.

Remember that window is the global namespace. These two lines attempt to declare the same variable:

window.APP = { ... }
const APP = window.APP

The second definition is not allowed in strict mode (enabled with 'use strict' at the top of your file).

To fix the problem, simply remove the const APP = declaration. The variable will still be accessible, as it belongs to the global namespace.

Identifier {X} has already been declared #365 it have product the correct result. i wanna use trycatch because if the browser does support  How to identify if a webpage is being loaded inside an iframe or directly into the browser window? 982. Browser: Identifier X has already been declared. 0.

I had a very close issue but in my case, it was Identifier 'e' has already been declared.

In my case caused because of using try {} catch (e) { var e = ... } where letter e is generated via minifier (uglifier).

So better solution could be use catch(ex){} (ex as an Excemption)

Hope somebody who searched with the similar question could find this question helpful.

Error with let: "Identifier '*' has already been declared" on REPL #8441 node > let x = foo ReferenceError: foo is not defined at repl:2:4 at sigintHandlersWrap (​vm.js:22:35) at Looks like an error in a browser, not in node. I'm using Google Chrome's Snippets (inside Dev Tools) for some JS development and testing. When declaring ES6 classes, the console throws an Uncaught SyntaxError: Identifier 'Foo' has already b

I write a library, using custom rendering and it works fine with node environment. However, it fails in browser environment demo index.js:1  Uncaught TypeError: Identifier 'APP' has already been declared and that is the whole file, I don't have that declare anywhere else in that file. But I have declared that var in the top of the other files.

The "const '{a}' has already been declared" error is thrown when JSHint encounters a with an identifier that has already been used in a previous constant declaration. /*jshint esnext: true */ const CONST_1 = 10; const CONST_1 = 20;. ​x. 1 However, since browser support for the const statement is limited and most  let broken = JSON.parse('I am broken'); > SyntaxError: Unexpected token I let broken = 5; > TypeError: Identifier 'broken' has already been declared let broken = 5; > TypeError: Identifier 'broken' has already been declared. I'm seeing this for a long time, but never took an effort to look into it more.

variable name occurs as a function parameter and is then redeclared "x" (​Firefox) SyntaxError: Identifier "x" has already been declared  Created with codeSandbox, but IPFS is buggy in codeSandbox (Identifier 'setImmediate' has already been declared) Clone this repo, then. npm i or yarn. npm start or yarn start. open developer tool (F12 or option + command + I) click the input and choose a file to upload. look at console.

Comments
  • window.APP = is an assignment, not a declaration. It's not even executed before the variable is declared.
  • This isn't quite strictly true. Globally-scoped let/const declarations in a real ES6 environment do not add a property to the global object but they do create global-scoped bindings.