Regex for the first 3 digits in a 6 digit number - regex

Question

I have items in a cms which have a 6-digit number.
The user can filter these item, via a input field,
by start typing a number.
const list = document.querySelector('#filter-wrap');
const searchBar = document.forms['search-kelim'].querySelector('input');
searchBar.addEventListener('keyup', function(e){
const term = e.target.value.toLowerCase();
const kelims = list.getElementsByClassName('filter-item');
Array.from(kelims).forEach(function(kelim){
let number = kelim.firstElementChild.textContent;
if(number.toLowerCase().indexOf(term) != -1 ){
console.log("Valid");
} else {
console.log("Invalid");
}
});
});
This is working, but it filters no matter where the digit
is occurring within the 6-digit number.
Aim is, it should only filter the first 3 starting digits, already starting with the first digit.
Meaning, if the user types 2, only the items starting with 2 are shown,
if the user then types 1, only the items starting with 21 are shown.
(the same for the third digit, typing 214 matches only the items starting with 214)
instead of indexof i tried with regex, but cannot get it to work:
var re = new RegExp("^[0-9]+$");
if (re.test(term)) {
console.log("Valid");
} else {
console.log("Invalid");
}
also tried these regex:
var re = new RegExp("^[0-9]");
var re = new RegExp("^\d{3}[0-9]");
var re = new RegExp("/[0-9]{1}[0-9]{1}[0-9]{1}/");
i also tried with match but also no luck, (different syntax?)
UPDATE:
here are two codepens for better understanding:
Filter with indexof, working but for first 3 digits.
https://codepen.io/hhentschel/pen/LYNWKeK
Filter with Regex, i tried all different answers, which came up so far.
https://codepen.io/hhentschel/pen/yLOMmbw

Answer 1

Your number variables all start with a line break. You may easily check that if you add console.log("'"+number+"': number") in the code.
To fix the regex approach, you just need to trim the incoming strings:
var re = new RegExp("^"+term);
if (re.test(number.trim())) { // <-- HERE!
kelim.classList.add("block");
kelim.classList.remove("hide");
} else {
kelim.classList.add("hide");
kelim.classList.remove("block");
}

Answer 2

Just check whether the Index is 0:
if(number.toLowerCase().indexOf(term) == 0){
console.log("Valid");
} else {
console.log("Invalid");
}
So you know that the term is at the beginning of the number.
But if you want to use regex, you have to build a new pattern every time:
var re = new RegExp("^"+term);
if (re.test(number)) {
console.log("Valid");
} else {
console.log("Invalid");
}