Check out example codes for "object map of the http parameters mutually exclusive with fromString". It will help you in understanding the concepts better.

Code Example 1

getCountries(data: any) {
    return this.httpClient.get("/api/countries", {params: data})
}

Code Example 2

let httpParams = new HttpParams({ fromObject: { aaa: 111, bbb: 222 } });

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