What does the code `(alert(1), "")` signify in the world of JavaScript programming?

Question

What does the code `(alert(1), "")` signify in the world of JavaScript programming?

While attempting the Google Gruyeres XSS challenges at , I encountered an interesting code snippet from their stored AJAX XSS challenge:

all <span style=display:none>"
+ (alert(1),"")
+ "</span>your base

The intriguing part is: (alert(1),"")

As per the solution provided, an empty string should be returned. However, in my testing, the alert(1) still executes.

Could this be some kind of function shorthand? Why does it trigger the alert, but then return an empty string?

I appreciate any guidance on this matter!

Warm regards,
Rolf

javascript ajax xss

Answer 1

Answer №1

Here we have the comma operator. In this code snippet, it first executes alert(1), then disregards its return value and proceeds to evaluate "". Since this is the final item in the expression sequence, it returns an empty string.

The provided tutorial explains the comma operator as follows:

In JavaScript, the comma operator evaluates each operand and ultimately gives back the value of the last one. You can combine multiple expressions using the comma operator.

Answer 2

Here we have the comma operator. In this code snippet, it first executes alert(1), then disregards its return value and proceeds to evaluate "". Since this is the final item in the expression sequence, it returns an empty string.

The provided tutorial explains the comma operator as follows:

In JavaScript, the comma operator evaluates each operand and ultimately gives back the value of the last one. You can combine multiple expressions using the comma operator.

What does the code `(alert(1), "")` signify in the world of JavaScript programming?

Answer №1

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