Format deep object to formData

form-data-builder.ts

class FormDataBuilder {
  static BuildObject2FormData<T>(obj: T): FormData {
    const formData: FormData = new FormData();

    if (obj == null) {
      return formData;
    }

    this.PopulateFormData(formData, '', obj);
    return formData;
  }

  private static PopulateArray<T>(params: FormData, prefix: string, val: Array<T>): void {
    val.forEach((prop, index) => {
      const key = prefix + '[' + index + ']';
      const value: any = val[index];
      this.PopulateFormData(params, key, value);
    });
  }

  private static PopulateObject<T>(params: FormData, prefix: string, val: T) {
    const objectKeys = Object.keys(val) as Array<keyof T>;

    if (prefix) {
      prefix = prefix + '.';
    }

    for (let prop of objectKeys) {
      const key = prefix + prop;
      const value = val[prop];
      this.PopulateFormData(params, key, value);
    };
  }

  private static PopulateFormData(params: FormData, key: string, value: any): void {
    if (this.isArray(value)) {
      this.PopulateArray(params, key, value);
    }
    else if (this.isDate(value)) {
      params.append(key, value.toISOString());
    }
    else if (this.isObject(value) && !this.isBlob(value) && !this.isFile(value)) {
      this.PopulateObject(params, key, value);
    }
    else {
      params.append(key, this.isNull(value) ? '' : value);
    }
  }

  private static isNull(value) {
    return value === null;
  }

  private static isArray(value) {
    return value instanceof Array;
  }

  private static isObject(value) {
    return value instanceof Object;
  }

  private static isDate(value) {
    return value instanceof Date;
  }

  private static isBlob(value) {
    return value &&
      typeof value.size === 'number' &&
      typeof value.type === 'string' &&
      typeof value.slice === 'function';
  }

  private static isFile(value) {
    return this.isBlob(value) &&
      (typeof value.lastModifiedDate === 'object'
        || typeof value.lastModified === 'number')
      && typeof value.name === 'string';
  }
}