cannot redeclare block scoped variable typescript

Question

I m building a node app  and inside each file in  js used to doing this to require in various packages   let co   require  co      But getting     etc  So using typescript it seems there can only be one such declaration require across the whole project   I m confused about this as I thought let was scoped to the current file   I just had a project that was working but after a refactor am now getting these errors all over the place   Can someone explain

User · Answer

In my case the following tsconfig json solved problem       quot compilerOptions quot          quot esModuleInterop quot   true       quot target quot    quot ES2020 quot        quot moduleResolution quot    quot node quot         There should be no type  module in package json

User · Answer

Use IIFE Immediately Invoked Function Expression   IIFE   function          all your code is here

User · Answer

For those coming here in this age  here is a simple solution to this issue  It at least worked for me in the backend  I haven t checked with the frontend code  Just add  export      at the top of your code  Credit to EUGENE MURAVITSKY

User · Answer

I got this error when upgrading   gulp-typescript          3 0 2          3 1 0  Putting it back to 3 0 2 fixed it

User · Answer

Regarding the error itself  let is used to declare local variables that exist in block scopes instead of function scopes  It s also more strict than var  so you can t do stuff like this   if  condition        let a   1              let a   2      Also note that case clauses inside switch blocks don t create their own block scopes  so you can t redeclare the same local variable across multiple cases without using    to create a block each     As for the import  you are probably getting this error because TypeScript doesn t recognize your files as actual modules  and seemingly model-level definitions end up being global definitions for it   Try importing an external module the standard ES6 way  which contains no explicit assignment  and should make TypeScript recognize your files correctly as modules   import   as co from    co    This will still result in a compile error if you have something named co already  as expected  For example  this is going to be an error   import   as co from    co      Error  import definition conflicts with local definition let co   1      If you are getting an error  cannot find module co      TypeScript is running full type-checking against modules  so if you don t have TS definitions for the module you are trying to import  e g  because it s a JS module without definition files   you can declare your module in a  d ts definition file that doesn t contain module-level exports   declare module  co        declare var co  any      export   co

User · Answer

I was receiving this similar error when compiling my Node JS Typescript application   node modules  types node index d ts 83 15 - error TS2451  Cannot redeclare block-scoped variable  custom    The fix was to remove this    files          node modules  types node index d ts      and to replace it with this    compilerOptions        types     node

User · Answer

The best explanation I could get is from Tamas Piro s post  TLDR  TypeScript uses the DOM typings for the global execution environment  In your case there is a  co  property on the global window object  To solve this    Rename the variable  or Use TypeScript modules  and add an empty export      export       or    Configure your compiler options by not adding DOM typings    Edit tsconfig json in the TypeScript project directory         quot compilerOptions quot              quot lib quot     quot es6 quot

User · Answer

In my case  using IntelliJ  File - Invalidate Caches   Restart    did the trick

User · Answer

I got the same problem  and my solution looks like this         module1 module1 ts  export module Module1       export class Module1          greating    return  hey from Module1                   module2 module2 ts  import  Module1  from       module1 module1    export module Module2      export class Module2          greating                let m1   new Module1 Module1               return  hey from Module2   and from loaded Model1     m1 greating                        Now we can use it on the server side         server ts       lt reference path    typings node node d ts   gt  import  Module2  from    module2 module2    export module Server       export class Server          greating                let m2   new Module2 Module2                return  hello from server  amp  loaded modules      m2 greating                       exports Server   Server        app js var Server   require    server   Server Server  var server   new Server    console log server greating       And on the client side too         public javscripts index index ts   import  Module2  from             module2 module2    document body onload   function        let m2   new Module2 Module2        alert m2 greating             views index jade extends layout  block content   h1  title   p Welcome to   title    script src  main js            the main js-file created by gulp-task  browserify  below in the gulpfile js   And  of course  a gulp-file for all of this         gulpfile js  var gulp   require  gulp        ts   require  gulp-typescript        runSequence   require  run-sequence        browserify   require  gulp-browserify        rename   require  gulp-rename     gulp task  default   function callback         gulp task  ts1   function             return gulp src     module1 module1 ts                 pipe ts                 pipe gulp dest    module1                 gulp task  ts2   function             return gulp src     module2 module2 ts                 pipe ts                 pipe gulp dest    module2                 gulp task  ts3   function             return gulp src     public javascripts index index ts                 pipe ts                 pipe gulp dest    public javascripts index                 gulp task  browserify   function             return gulp src    public javascripts index index js     read  false                 pipe browserify                   insertGlobals  true                              pipe rename  main js                 pipe gulp dest    public javascripts                  runSequence  ts1    ts2    ts3    browserify   callback        Updated  Of course  it s not neccessary to compile typescript files separatly  runSequence   ts1    ts2    ts3     browserify   callback  works perfect

[typescript] cannot redeclare block scoped variable (typescript)

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