Question

I have following code in java script

    var regexp = /\$[A-Z]+[0-9]+/g;
    for (var i = 0; i < 6; i++) {
        if (regexp.test("$A1")) {
            console.log("Matched");
        }
        else {
            console.log("Unmatched");
        }
    }

Please run it on your browser console. It will print alternative Matched and Unmatched. Can anyone tell the reason for it.

Answer 1

After call test on a string, the lastIndex pointer will be set after the match.

Before:
$A1
^

After:
$A1
   ^

and when it comes to the end, the pointer will be reset to the start of the string.

You can try ‘$A1$A1’, the result will be

Matched
Matched
Unmatched
...

This behavior is defined in 15.10.6.2, ECMAScript Language Spec.

Step 11. If global is true,
a. Call the [[Put]] internal method of R with arguments “lastIndex“, e, and true.