Why `pattern.test(name)` opposite results on consecutive calls [duplicate]

Question

Why is this code returning first true, then false

var pattern = new RegExp("mstea", 'gi'), name = "Amanda Olmstead";

console.log('1', pattern.test(name));
console.log('1', pattern.test(name));

Demo: Fiddle

Answer 1

g is for repeating searches. It changes the regular expression object into an iterator. If you want to use the test function to check your string is valid according to your pattern, remove this modifier :

var pattern = new RegExp("mstea", 'i'), name = "Amanda Olmstead";

The test function, contrary to replace or match doesn't consume the whole iteration, which lets it in a "bad" state. You should probably never use this modifier when using the test function.

Answer 2

You don't want to use gi in combination with pattern.test. The g flag means that it keeps track of where you are running so it can be reused. So instead, you should use:

var pattern = new RegExp("mstea", 'i'), name = "Amanda Olmstead";

console.log('1', pattern.test(name));
console.log('1', pattern.test(name));

Also, you can use /.../[flags] syntax for regex, like so:

var pattern = /mstea/i;