CODE EXAMPLE FOR JAVASCRIPT

file upload in angular 10

onFileChange(event) {
    const reader = new FileReader();

    if (event.target.files && event.target.files.length) {
      const [file] = event.target.files;
      reader.readAsDataURL(file);
      reader.onload = () => {
        this.data.parentForm.patchValue({
          tso: reader.result
        });

        // need to run CD since file load runs outside of zone
        this.cd.markForCheck();
      };
    }
  }