Question 108496 in Javascript Question posted in
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Javascript – How to check elements type

I need help )

enter image description here

return (
        <ButtonWrapperStyled>
            <input {...getInputProps()} />
            <Button {...getRootProps()}>Загрузить</Button>

            {files.map((file) => {//file maybe FileProps or File type
                if (file) {// How can I check file type here?
                    return <div>{file.fileId}</div>
                } else {
                    return <div>{file.fileId}</div>
                }
            })}
        </ButtonWrapperStyled>
)

I typed array, it may be FileProps or File type.
How can I check it correctly in files.map?

I can’t resolve this issue

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2

Answers


  1. Chosen as BEST ANSWER
    0 
    // This option doesn't work, why?
{files.map((file) => {
    if (file?.fileId) {
        return <div>{file.fileName}</div>
    } else {
        return <div>{file.name}</div>
    }
})}
//This option works
{files.map((file) => {
    if ('fileId' in file) {
        return <div>{file.fileName}</div>
    } else {
        return <div>{file.name}</div>
    }
})}

  2. 0

    You need to use type guards Type Guards and Differentiating Types

    type File = {
  fileId: number;
};

type FileProps = {
  name: string;
  size: number;
};

const files: (FileProps | File)[] = [];

files.map((file) => {
  if ('fileId' in file) {
    return <div>{file.fileId}</div>;
  } else {
    return <div>{file.name}</div>;
  }
}, []);
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