Why can't we have return in the ternary operator?

The ternary operator evaluates to an expression and expressions can't contain a return statement (how would that behave if you were to assign the expression to a variable?). However, you could very well return the result of a ternary operator, i.e. return condition? returnValue1 : returnValue2;

On your specific point, I don't see why you would like to return. It looks like you're trying to do something only if a condition is fulfilled. A simple if statement would probably be more adequate there.

JavaScript (like many other languages) has expressions and statements. An expression must evaluate to something. A statement performs an action. Expressions can be used as statements, but the reverse is not true.

return is a statement. It does not evaluate to anything. You are using a ternary expression (a.k.a ternary operator), which has the syntax

test ? expression1 : expression2

and evaluates to expression1 if the condition holds, and expression2 otherwise. This implies that expression1 and expression2 must themselves evaluate to something, and cannot be statements.

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Bottom line, you should use an if.

Because it is not syntactically correct. Here's the correct syntax for a ternary operator -

condition ? expr1 : expr2 

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator

And return is not part of an expression. return is followed by an expression. (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/return)