I asked this question earlier, and after thinking about the topic some more, I began to wonder where the seemingly fuzzy boundary between the meanings of the terms “statement” and “expression” lies. Are all statements also expressions? Where do the return values in a REPL console come from? They don’t always seem to make any intuitive sense. Of course, if you type 1+1, you’ll get 2, but other times it isn’t as obvious what the logic is.
Given that anything typed into REPL produces some value, does it mean that it can be used in JS source code as both an expression and a standalone statement?
Can the string of code that could be used for _X_ in the following snippet also be used for _Y_ and vice versa? if(_X_) _Y_?
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Answer
Are all statements also expressions?
“Wherever JavaScript expects a statement, you can also write an expression. Such a statement is called an expression statement. The reverse does not hold: you cannot write a statement where JavaScript expects an expression. For example, an if statement cannot become the argument of a function.”
This is comes from a recent post by Axel Rauschmayer about this topic: Expressions versus statements in JavaScript
Hope it helps.