A template expression produces a value similar to any Javascript expression. Angular executes the expression and assigns it to a property of a binding target; the target might be an HTML element, a component, or a directive. In the property binding, a template expression appears in quotes to the right of the = symbol as in [property]="expression". In interpolation syntax, the template expression is surrounded by double curly braces. For example, in the below interpolation, the template expression is {{username}},
<h3>{{username}}, welcome to Angular</h3>
The below javascript expressions are prohibited in template expression
assignments (=, +=, -=, ...)
new
chaining expressions with ; or ,
increment and decrement operators (++ and --)
