Plugin not installed says while saving file using cordova-plugin-file

[shivakanthredd]

i've installed cordova-plugin-file but it is showing plugin is not installed while saving the file. i've used platform ready function also.

this.platform.ready().then((err)=>{ console.log(err); let result=this.file.createDir(this.file.externalRootDirectory,this.fileDir,true);

result.then( data=> {
    this.dirPath=data.toURL();
    alert("dir created"+ this.dirPath);
    this.file.writeFile(this.dirPath, this.fileName, this.fileContent, {replace:true});
    alert("file created"+ this.dirPath);

}).catch(error => {
  alert(error);
});

});