Javascript to interact with Dynamics 365 SDK

clientside.js

var Sdk = window.Sdk || {}

Sdk.request = function (action, uri, data, formattedValue, maxPageSize) {
    if (!RegExp(action, "g").test("POST PATCH PUT GET DELETE")) { // Expected action verbs.
        throw new Error("Sdk.request: action parameter must be one of the following: " +
            "POST, PATCH, PUT, GET, or DELETE.");
    }
    if (!typeof uri === "string") {
        throw new Error("Sdk.request: uri parameter must be a string.");
    }
    if ((RegExp(action, "g").test("POST PATCH PUT")) && (data === null || data === undefined)) {
        throw new Error("Sdk.request: data parameter must not be null for operations that create or modify data.");
    }
    if (maxPageSize === null || maxPageSize === undefined) {
        maxPageSize = 10; // Default limit is 10 entities per page.
    }

    // Construct a fully qualified URI if a relative URI is passed in.
    if (uri.charAt(0) === "/") {
        uri = clientUrl + webAPIPath + uri;
    }

    return new Promise(function (resolve, reject) {
        var request = new XMLHttpRequest(); 
        request.open(action, encodeURI(uri), true);
        request.setRequestHeader("OData-MaxVersion", "4.0");
        request.setRequestHeader("OData-Version", "4.0");
        request.setRequestHeader("Accept", "application/json");
        request.setRequestHeader("Content-Type", "application/json; charset=utf-8");
        request.setRequestHeader("Prefer", "odata.maxpagesize=" + maxPageSize);
        if (formattedValue) {
            request.setRequestHeader("Prefer",
                "odata.include-annotations=OData.Community.Display.V1.FormattedValue");
        }
        request.onreadystatechange = function () {
            if (this.readyState === 4) {
                request.onreadystatechange = null;
                switch (this.status) {
                    case 200: // Success with content returned in response body.
                    case 204: // Success with no content returned in response body.
                        resolve(this);
                        break;
                    default: // All other statuses are unexpected so are treated like errors.
                        var error;
                        try {
                            error = JSON.parse(request.response).error;
                        } catch (e) {
                            error = new Error("Unexpected Error");
                        }
                        reject(error);
                        break;
                }
            }
        };
        request.send(JSON.stringify(data));
    });
};

var url = Xrm.Page.context.getClientUrl() + "/api/data/v8.2/contacts?$filter=firstname eq 'Sean'&$select=fullname";

Sdk.request("GET", url, null, true)
	.then(function (request) {
		var collection = JSON.parse(request.response).value;
		for(var i=0;i<collection.length;i++){
			console.log(collection[i]["fullname"]);
		}
    });