Thanks, Derek. Actually, my code snippet is pretty much like the sample code, which initializes esriRequest's parameters in declaration.
function getStuff() {
var restURL = "http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Demographics/ESRI_Census_USA/MapServer/layers";
var myRequest = esriRequest({
url: restURL,
content: {f: "json"},
handleAs: "json",
callbackParamName: 'callback'
});
myRequest.then(requestSucceeded, requestFailed); // Problem!
function requestSucceeded(response, io){
alert("Success");
}
function requestFailed(error, io){
alert("Error");
}
Still puzzled about why it's complaining about 'then'...