React Native [TypeError：无法读取未定义的属性'startsWith']？

Question

I'm getting this error when I put my Javascipt code to a Typescript project. In Javascript project its worked fine but when I put the code into a Typescript project I got the error.

Is there any mistake in coding?

Here's the code :

const createPDF = async() => {
    let Options = {
      html: '<h1>test</h1>',
      fileName: 'test',
      directory: 'Download',
    };

    let file = await RNHTMLtoPDF.convert(Options)
    Alert.alert('Alert','Successfully exported file:' + file.filePath,[
      {text:'Cancel',style:'cancel'},
      {text:'Open',onPress:()=>openFile(file.filepath)}
    ],{cancelable:true});
  }

  const openFile = (filepath: any) => {
    const path = filepath;
    FileViewer.open(path)
    .then(()=>{
      //success
      console.log(`Successfully export PDF file`);
      
    })
    .catch(error => {
      console.log(error);
    });
  }

LOG      [TypeError: Cannot read property 'startsWith' of undefined]

Answer 1

finally I have solved the problem by adding string type and :void to filepath instead of any ( i dont know what this mean but it worked )

  const openFile = (filepath: string):void => {
    const path = filepath;
    FileViewer.open(path, { showOpenWithDialog: true })
    .then(()=>{
      //success
      console.log(`Successfully export PDF file`);
      
    })
    .catch(error => {
      console.log(error);
    });
  }