Get lookup text using WEB API
Following code will fetch the originating lead lookup text and Id from an opportunity .
var req = new XMLHttpRequest(); req.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v8.0/opportunities?$select=_originatingleadid_value&$filter=_originatingleadid_value ne null", true); req.setRequestHeader("OData-MaxVersion", "4.0"); req.setRequestHeader("OData-Version", "4.0"); req.setRequestHeader("Accept", "application/json"); req.setRequestHeader("Content-Type", "application/json; charset=utf-8"); req.setRequestHeader("Prefer", "odata.include-annotations=\"OData.Community.Display.V1.FormattedValue\""); req.onreadystatechange = function () { if (this.readyState === 4) { req.onreadystatechange = null; if (this.status === 200) { var results = JSON.parse(this.response); for (var i = 0; i < results.value.length; i++) { var _originatingleadid_value = results.value[i]["_originatingleadid_value"];// Id var _originatingleadid_value_formatted = results.value[i]["_originatingleadid_value@OData.Community.Display.V1.FormattedValue"];// text value } } else { alert(this.statusText); } } }; req.send();