Symptoms

Client-side rewriting may give incorrect results for JavaScript assignment operators if left-hand operand is index expression or dot expression: a[i]-=b; a.value*=c;

Impact

Any JavaScript code with arithmetic assignment operators may work incorrectly.

Conditions

Assignment operators -=, *=, /=, %= are handled incorrectly if the result is assigned to index expression (like a[i]) or dot expression (like a.value). The effect occurs only if JavaScript code is inside 'eval' statement or is generated by write/writeln functions. Rewritten code does not include arithmetic operation which leads to incorrect values.

Workaround

Replace arithmetic assignment operators by pairs of simple assignment and arithmetic operation, for example: a[i] -= b --> a[i] = a[i] - b

Fix Information

Now JavaScript arithmetic assignment operators are handled correctly on the server and on the client.

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips