javascript/jQuery regular expressions?

https://regex101.com/r/eA3bF9/3
Have a look.

that is a cool tool!

It should ONLY allow those combination types..

xf1234 sent back a true.. which is no good.. ?? x1234 good, xD44444 is no good.

Is it an easy change to tweak it to only allow that list?

Try now: https://regex101.com/r/eA3bF9/4
click on the left "Unit tests" and play

The goal is to "Match"

I will remove leading whitespace then just below (except that 12345.. means [0-9]{1,10}
they want to allow
' ext. 12345 '
'ext 123456789'
' Ext. 1234567 '
'Ext 1234'
'x123456'

I thought this would do it..
(x{1}|ext{1}|ext\.{1}|Ext{1}|Ext\.{1})\s*[0-9]{1,}

Here, I tweaked it because you gave me this cool tool!

(?:\s*(?:x|ext\.?)\s*(\d{1,10})+)?

But now I want to exclude this one
ext.    5t64564

I want the digits to be the last part of the input.. no extra chars

I only want it to match those patterns. only is a + sign ?

It already does what you want, not sure what you are doing.
just add ^ at start and $ at the end. Like this.
^(?:\s*(?:x|ext\.?)\s*(\d{1,10})+)?$
Use "Unit tests" to create tests and test with real values, my list in "Test string" doesn't make any sense as there are many stringS, it just for personal preview that it works.

Why doesn't the tool match any with that?
^(?:\s*(?:x|ext\.?)\s*(\d{1,10})+)?$

I tried
^(x|ext\.?\s)?[0-9]{3,10}$ in the tool but doesn't match anything.

tried this in the console and worked great.. (except for matching Ext and Ext.)
var myExp = /^(x|ext\.?\s)?[0-9]{3,10}$/;
if (myExp.test("ext. 123")){
    console.log('true');
}else{
    console.log('false');
}

Use "Unit tests" to create tests and test with real values, my list in "Test string" doesn't make any sense as there are many stringS, it just for personal preview that it works.

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ahh didn't read this.. looks good! thanks!

Awesome! thanks for the help!