Getting text before a character in a string in Javascript

Using Jquery text() you can get the expected value

$(document).ready(function(){
  const innerHTMl = $(".am-event-sub-info").text();
  console.log(innerHTMl.split('-')[0]);
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="#am-events-booking">

<div class="am-event-info">
  <div class="am-event-sub-info">
    <div class="am-event-sub-info-capacity"><img src=""> Capacity: 0 / 100</div>
    <!---->
  </div>
  <div class="am-event-sub-info">
    <div><img src="">February 27th, 2021 11:30 am - 1:00 pm</div>
  </div>
</div>
</div>

There are two ways to approach this answer.

Example One:

let date = "February 27th, 2021 11:30 am - 1:00 pm";
let extractDate = date.substr(0, date.indexOf('-')); 
console.log(extractDate);

Example Two:

let date = "February 27th, 2021 11:30 am - 1:00 pm";
let extractDate = date.split('-')[0]; 
console.log(extractDate);

The error is caused because the string that you are trying to split is undefined, that being because thast jQuery syntax won't properly return what you expect.

There are two other problems:

1. There are multiple am-event-info divs. I took account of that in the code below
2. You are trying to parse an irregular date string, which is actually a time range.

I propose you a pure js solution, in which we first identify all the am-event-sub-info divs, iterate through them, check if they contain a date and if so, operate on that date:

    let dates = document.querySelectorAll('.am-event-sub-info');

    dates.forEach(function(e) {
    
    let dateString = e.innerText;

    if (!isNaN(Date.parse(dateString))) {

        let date = new Intl.DateTimeFormat('en-US', {
            weekday: 'long'
        }).format(
            new Date(dateString)
        )

        //do something with "date"
        console.log(date);

    }

})

But as your date string is of an irregular format, if you want the above to work, you need to do something about it. If you're only interested in the date itself, convert let dateString to a valid date with some regex, this will make the below the functioning code:

let dates = document.querySelectorAll('.am-event-sub-info');

dates.forEach(function (e) {

    var dateString = e.innerText;
    let re = /(\w+) (\d{1,2}\w\w), (\d\d\d\d)/;
    if (re.test(dateString)) {
        var match = re.exec(dateString);
        let day = /\d{1,}/.exec(match[2])
        let month = match[1].slice(0, 3);
        let year = match[3];
        let dt = new Date(Number(day, month, year));

        //dt is now your full date

        let date = new Intl.DateTimeFormat('en-US', {
            weekday: 'long'
        }).format(dt)

        //do something with your formatted "date"
        console.log(date);

    }

})