144
rated 0 times
[
149]
[
5]
/ answers: 1 / hits: 6627
/ 10 Years ago, thu, june 5, 2014, 12:00:00
Steps:
Open page in Firefox 29.0.1 (Windows 7 x64):
<!doctype html>
<title>Test</title>
<script>
(function () {
var x = 5, f = function () {
setTimeout(f, 1000);
};
f();
}());
</script>
Open Developer Tools (F12).
In the Debugger, set a breakpoint on:
setTimeout(f, 1000);Once the breakpoint is hit, evaluate
xin the console. The result:undefined
Reload the page. The breakpoint is hit on the first run of
f.Evaluate
x. The result:5Resume execution, and when the breakpoint is hit again, evaluate
x. Same result:5
My assumption: If Firefox realizes on the first run of f that x is not needed, then it doesn't store the value of x with f. So in subsequent calls to f the value of x is undefined. Interestingly, I see the same behavior in Chrome 35 and IE11.
Question: What is going on? Can I configure Firefox to make x evaluate to its correct value in step 4 (see above)?
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