I am trying to use typescript and express for my app. I wrote a function that I wish to use in multiple places. I called the function, I can see the values when I use console.log, however, I can't access the values. It is telling me that the value does not exist on the type: Here is my code:

 export const httpIUploadImage = async(req: Request, res: Response,)=>{
 
    const fileString = req?.file?.path

    if(!fileString){
        return res.status(404).json('no image found');
    }

    const uploadResponse = await cloudinaryUpload(fileString);
   

    const result = {
        url: uploadResponse.secure_url,
        publicId: uploadResponse.public_id
        }

  return result

  
 }catch(err){
  return res.status(500).json(err)
 }
 }

I used it here:

export const httpCreateCategory = async(req: Request, res: Response)=>{

 }
 const imageResult = await httpIUploadImage(req, res);
 console.log(image)//I can see the object and the values which is {url: value, publicId: value}
 
 const url = imageResult.url// This throws type error telling me that url does not exist

How Do I fix this?

CodePudding user response：

Because Typescript can not apply type inference for your function as you have multiple return types.

So you need to add a return type on your function definition:

type ImageResultType = {url: string, publicId: string}
export const httpIUploadImage = async(req: Request, res: Response): Promise<ImageResultType | ResponseType>

After the function call you will need to check its type with type guards

 function isResult(resType: ImageResultType | ResponseType): resType is ImageResultType {
  return (resType as ImageResultType).url !== undefined;
}

This way you can handle your errors better with writing an else block

if(isResult(imageResult))
    imageResult.url

Also I recommend to check type inference type guards