JavaScript: What causes the error: Uncaught TypeError: Cannot read property '1' of null?

Question

JavaScript

Good afternoon!
Can you please tell me what is causing the error: Uncaught TypeError: Cannot read property '1' of null?

var as = document.getElementsByTagName('a');
var re = /^https?:\/\/([^\/]*)\//;
for (var i = 0, l = as.length; i < l; i++) {
    var href = as[i].href;
    var matches = href.match(re);
    if (matches[1] && matches[1] != "mysite") {
        as[i].setAttribute("target","_blank");
    }
}

Answer 1

The error occurs because the matches variable is null. Most likely one of the links has a curved href. Accordingly, match(...) does not find matches and returns null. Before using the result of this method, check what it returned.

Answer 2

Because there is no second element in the matches array now.