wanderer/assets/js/hooks/Mapper/utils/loadTextFile.ts

export function loadTextFile(): Promise<string> {
  return new Promise((resolve, reject) => {
    const input = document.createElement('input');
    input.type = 'file';
    input.accept = 'application/json,.json';

    input.onchange = () => {
      const file = input.files?.[0];
      if (!file) {
        reject(new Error('No file selected'));
        return;
      }

      const reader = new FileReader();
      reader.onload = () => {
        resolve(reader.result as string);
      };
      reader.onerror = () => {
        reject(reader.error);
      };

      reader.readAsText(file);
    };

    input.click();
  });
}