/*
For Letters: [a-zA-Z] (dealing with both upper and lower case characters)
For Space: [ ]
Putting them together: [a-zA-Z ]+
Use a + instead of * since a blank string is not a valid letter nor a space.
Use ^ and $ since our string should start and end with the given pattern.
*/
var myStr = "hello";
if(/^[a-zA-Z ]+$/.test(myStr) {
  window.alert("String contains only alphabets and spaces");
} else {
  window.alert("String doesn't contain only alphabets and spaces");
}