The page I am working on has a javascript function executed to print parts of the page. For some reason, printing in Safari, causes the window to somehow update. I say somehow, because it does not really refresh as in reload the page, but rather it starts the "rendering" of the page from start, i.e. scroll to top, flash animations start from 0, and so forth. The effect is reproduced by this fiddle: http://jsfiddle.net/fYmnB/ Clicking the print button and finishing or cancelling a print in Safari causes the screen to "go white" for a sec, which in my real website manifests itself as something "like" a reload. While running print button with, let's say, Firefox, just opens and closes the print dialogue without affecting the fiddle page in any way. Is there something with my way of calling the browsers print method that causes this, or how can it be explained - and preferably, avoided? P.S.: On my real site the same occurs with Chrome. In the ex
To workaround the problem, you can remove the g flag or reset lastIndex as in
ReplyDeletevar reg = /a/g;
console.log(reg.test("a"));
reg.lastIndex = 0;
console.log(reg.test("a"));
The problem arises because test is based around exec which looks for more matches after the first if passed the same string and the g flag is present.
15.10.6.3 RegExp.prototype.test(string) # Ⓣ Ⓡ
The following steps are taken:
Let match be the result of evaluating the RegExp.prototype.exec (15.10.6.2) algorithm upon this RegExp object using string as the argument.
If match is not null, then return true; else return false.
The key part of exec is step 6 of 15.10.6.2:
6. Let global be the result of calling the [[Get]] internal method of R with argument "global".
7. If global is false, then let i = 0.
When i is not reset to 0, then exec (and therefore test) does not start looking at the beginning of the string.
This is useful for exec because you can loop to handle each match:
var myRegex = /o/g;
var myString = "fooo";
for (var match; match = myRegex.exec(myString);) {
alert(match + " at " + myRegex.lastIndex);
}
but obviously it isn't so useful for test.
Usually a test is chosen to check if some pattern matches at all, but the global flag lets you loop through a string to either count the matches or,like exec, do something with each lastIndex. Another use is to set the lastIndex of the rx yourself before the test is peformed, to ignore matches before some character index.
ReplyDeletevar count=0, rx=/\s+/g, rx.lastIndex=100;
while(rx.test(string))count++;