Automatic semicolon insertion & return statements

Question

As you might know, ECMAscript tries to be smart and will automatically insert semicolons if you didn't write those explicitly. Simple example ``` function foo() { var bar = 5 return bar } ``` will still work as expected. But there are some caveats if you rely on that. If we re-write that function like so ``` function foo() { var bar = 5 return { bar: bar } } ``` ..that function would now return `undefined` because the interpreter would insert that semicolon right after the `return` statement (that's a reason why you always should bring curly brackets on the same line as a statement). However, knowing all this I'm wondering now how safe a `return` statement like the following is, across browsers and versions ``` function foo() { var a = true, b = true, c = false; return a && b && c; } ``` I just wrote a similar `return statement` in a production environment. Just because I knew about the "problems" with ECMAscript beeing not-so-smart about semicolon insertion I'm wondering now, if that…

Accepted Answer

The javascript interpreter/compiler is so smart to only insert automatic semicolons if afterwards there is valid Javascript.

Your code works, because `&& b` as it stands is no valid expression - that's why no semicolon gets inserted after the `return a` resulting in:

```
return a && b && c;
```

However:

```
return (undefined);//implicitely inserted
{
    ....
}
```

is perfectly valid and thats why a semicolon gets inserted.

For completeness' sake the ref to the spec: automatic semicolon insertion. THe examples are worth reading through.

Automatic semicolon insertion & return statements

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