@niivue/niivue/src/utils/file-utils.ts

minimal webgl2 nifti image viewer

export function readFileAsDataURL(input: File | FileSystemFileEntry): Promise<string> {
    return new Promise<string>((resolve, reject) => {
        let filePromise: Promise<File>

        if (input instanceof File) {
            filePromise = Promise.resolve(input)
        } else {
            filePromise = new Promise<File>((resolve, reject) => {
                input.file(resolve, reject)
            })
        }

        filePromise
            .then((file) => {
                const reader = new FileReader()

                reader.onload = (): void => {
                    if (typeof reader.result === 'string') {
                        resolve(reader.result)
                    } else {
                        reject(new Error('Expected a string from FileReader.result'))
                    }
                }

                reader.onerror = (): void => {
                    reject(reader.error ?? new Error('Unknown FileReader error'))
                }

                reader.readAsDataURL(file)
            })
            .catch((err) => reject(err))
    })
}