js types can only be used in a ts file - Visual Studio Code using ts-check

Question

I am starting to use TypeScript in a Node project I am working on in Visual Studio Code  I wanted to follow the  opt-in  strategy  similar to Flow  Therefore I put     ts-check at the top of my  js file in hope to enable TS for that file  Ultimately I want the same experience of  linting  as Flow  therefore I installed the plugin TSLint so I could see Intellisense warnings errors   But with my file looking like       ts-check  module exports       someMethod   param  string   string   gt        return param            and my tsconfig json file looking like          compilerOptions            target    es2016          module    commonjs          allowJs   true         I get this error   js   types  can only be used in a  ts file  as shown below in the image     I saw this question which recommended disabling javascript validation in vscode but then that doesn t show me any TypeScript Intellisense info   I tried setting tslint jsEnable to true in my vscode settings as mentioned in the TSLint extension docs but no luck there   What is the correct setup in order to use  js files with TypeScript and get Intellisense so I know what the errors in my code are before I run any TS commands

User · Answer

Use  javascript validate enable   false in your VS Code settings  It doesn t disable ESLINT  I use both ESLINT  amp  Flow  Simply follow the instructions Flow For Vs Code Setup  Adding this line in settings json  Helps  javascript validate enable   false

User · Answer

You must use a  ts file - e g  test ts to get Typescript validation  intellisense typing of vars  return types  as well as  typed  error checking  e g  passing a string to a method that expects an number param will error out    It will be transpiled into  standard   js via tsc     Update  11 2018    Clarification needed based on down-votes  very helpful comments and other answers   types   Yes  you can do type checking in VS Code in  js files with  ts-check - as shown in the animation What I originally was referring to for Typescript types is something like this in  ts which isn t quite the same thing   hello-world ts  function hello str  string   string     return 1     function foo str string  void     console log str       This will not compile  Error  Type  1  is not assignable to String if you tried this syntax in a Javascript hello-world js file      ts-check  function hello str  string   string     return 1     function foo str string  void     console log str       The error message referenced by OP is shown   js   types  can only be used in a  ts file   If there s something I missed that covers this as well as the OP s context  please add  Let s all learn

User · Answer

For anyone who lands here and all the other solutions did not work give this a try  I am using typescript   react and my problem was that I was associating the files in vscode as javascriptreact not typescriptreact so check your settings for the following entries        files associations            tsx    typescriptreact          ts    typescriptreact

User · Answer

I m using flow with vscode but had the same problem   I solved it with these steps   Install the extension Flow Language Support  Disable the built-in TypeScript extension   Go to Extensions tab Search for  builtin TypeScript and JavaScript Language Features Click on Disable

User · Answer

Just default the variable to the expected type   number 1    gt       number 1 0    gt       string  str

[javascript] js 'types' can only be used in a .ts file - Visual Studio Code using @ts-check

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