Javascript – js ‘types’ can only be used in a .ts file – Visual Studio Code using @ts-check

javascripttypescriptvisual-studio-code

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 => {
    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?

Best 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:
1. Go to Extensions tab
2. Search for @builtin TypeScript and JavaScript Language Features
3. Click on Disable

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The # symbol identifies the ID of the element. Use .text() to set the inner text.

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You have

char *array[size];

That makes array an array of pointers. Specifically, array is an array of size pointers. Each element in the array (array[0] to array[size-1]) is of type char *.

I think it would help if you understood how array works:

+-------+-------+-------+-------+
|  [0]  |  [1]  |  [2]  |  [3]  |
+-------+-------+-------+-------+
    |       |       |       |
    |       |       |       |
    |       |       |       |
    v       v       v       v

Each of the boxes above represents a pointer, and the arrows are where they are pointing to. The storage for them is not yet assigned to, so they are just "out there", pointing nowhere useful. You can either create memory for them (malloc() etc., in C, new[] in C++), or you can point them to some existing location.

You say:

...put some strings in it. If I assign something again to them, they don't replace the previous contents but they keep on appending on the previous contents. How do I correctly clear/reset all of its contents?

It is not clear how you are putting "strings in it". Do you mean you are storing strings in array[0]..array[size-1]? How? Are you assigning literal strings to them? Something like:

array[0] = "String";

If you are doing that, then, you can reassign to the pointers and the strings wouldn't append. In other words, if later in your program you do:

array[0] = "Another string";

you are reassigning the pointer array[0] to point to "Another string", and thus you're not appending.

So, in short, we need to see more code, and you may need to understand pointers and arrays better.

Edit: Based upon your edit, the pointers myMainArr[i] (for i=0 to i=3), do get reassigned to the corresponding elements from myArrOne or myArrOne (not a typo!), depending upon the contents of action. So, if you printed them (for example, printf("%s\n", myMainArr[0]);), you shouldn't see any strings being appended. Also, myMainArr is local to your function function, so it gets destroyed when your function returns. (Incidentally, your choice of the names array for an array and function for a function make it harder to be unambiguous when answering the question!)

If you are having a problem, please post a complete, minimal, compilable code that shows the problem.

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