Why doesn't this eval call alert("Summer")?

eval('(caption="Summer";alert(caption))');

Does it have something to do with the quotes in "Summer"?

Why doesn't this eval call alert("Summer")?

eval('(caption="Summer";alert(caption))');

Does it have something to do with the quotes in "Summer"?

• javascript
• eval

• Why do you have parentheses around all the stuff inside the quotes? – Anon. Commented Feb 14, 2010 at 23:35
• If you want to sequence statements inside an expression use the , operator: eval('(caption="Summer",alert(caption))'); – Dominic Cooney Commented Feb 15, 2010 at 0:50

4 Answers 4

Uncaught SyntaxError: Unexpected token ;

The outer parentheses make no syntactical sense. Try this:

eval('caption="Summer";alert(caption)');

Chrome console:

eval('(caption="Summer";alert(caption))')
SyntaxError: Unexpected token ;

This works:

eval('caption="Summer"; alert(caption)')

The extra parentheses are wrong, this is correct:

eval('caption="Summer";alert(caption)');

A more better way to do this and avoid syntax problem is to do following,

eval(function(){var x="test"; alert(x)}());