On page 39 of chapter 3, the text below the code for the insert function specifies shift(). It should be corrected to splice() as per the code example.
function insert(element, after) {
var insertPos = this.find(after);
if(insertPos > -1) {
this.dataStore.splice(insertPos+1, 0, element);
++this.listSize;
return true;
}
return false;
}