<input type="file" multiple (change)="onSelectedFile($event)"/>

images = [];
onSelectedFile(e){
    let listUrl = this.images.map(image => image["url"]);
    const files = e.target.files;
    let selectedFiles = [];
    for (let i = 0; i < files.length; i++) {
      let reader = new FileReader();
      reader.onload = e =>
        selectedFiles.push({ file: files[i], url: reader.result });
      reader.readAsDataURL(files[i]);
    }
    console.log(selectedFiles);
    console.log(selectedFiles.length);
    let fileDistinct = selectedFiles.filter(x => listUrl.indexOf(x.url) < 0);
    if(fileDistinct.length > 0){
      this.images = [...this.images, ...fileDistinct]
    }
}