Sample WebAPI Methods for MSCRM 2016

function InitiateAPICalls() {
    var resp = ExecuteAPIRequest("accounts"); //Ajax Request
    var resp1 = ExecuteXmlRequestToAPI("accounts"); //XMLHttpRequest

}


function result(resultArray, error) {
    this.results = resultArray;
    this.error = error;
}
function ExecuteAPIRequest(query) {
    var resultArray = null;
    var errorMessage = null;
    $.ajax(
    {
        type: "GET",
        url: Xrm.Page.context.getClientUrl() + "/api/data/v8.0/" +query,
        async: false,
        headers: { "Accept": "application/json", "Content-Type": "application/json;charset=utf-8", "OData-MaxVersion": "4.0", "OData-Version": "4.0" }
    })
    .done(function (Httpresponse) {
        resultArray = Httpresponse.value;
    })
    .fail(function (Httpresponse) {
        var errors = JSON.parse(Httpresponse.responseText);
        if (errors.error)
            errorMessage = "There was an error executing the request. " + Httpresponse.status + " " + Httpresponse.statusText +". " + errors.error.message;
    })
    .always(function (Httpresponse) {
    });
    return new result(resultArray,errorMessage);
}

function ExecuteXmlRequestToAPI(query) {
    var resultArray = null;
    var errorMessage = null;
    var req = new XMLHttpRequest()
    var resultArray = null;
    req.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v8.0/"+ query, false);
    req.setRequestHeader("Accept", "application/json");
    req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
    req.setRequestHeader("OData-MaxVersion", "4.0");
    req.setRequestHeader("OData-Version", "4.0");
    req.onerror = function (error) {
        throw new Error("There was an error executing the request. " + req.status + " " + error.message);
    }
    var response = req.send();
    if (req.status == 200) {
        var results = JSON.parse(req.response);
        resultArray = results.value;
    }
    else {
        var errors = JSON.parse(req.response);
        if (errors.error)
            errorMessage = "There was an error executing the request. " + req.status + " " +req.statusText+ ". "+ errors.error.message;
    }
    return new result(resultArray,errorMessage);
}