You may try a regex string split here:

var inputs = ["£____", "____$", "42____$"];
for (var i=0; i < inputs.length; ++i) {
    var parts = inputs[i].split(/_+/);
    console.log("before = " + parts[0] + ", after = " + parts[1]);
}

const streetAddress = addy.substring(0, addy.indexOf(","));

While it’s not the best place for definitive information on what each method does (MDN Web Docs are better for that) W3Schools.com is good for introducing you to syntax.

Do you mean substring instead of subscript? If so. Then yes.

var string = "55+5"; // Just a variable for your input.

function getBeforePlus(str){

    return str.substring(0, str.indexOf("+")); 
   /* This gets a substring from the beginning of the string 
      to the first index of the character "+".
   */

}

Otherwise, I recommend using the String.split() method.

You can use that like so.

var string = "55+5"; // Just a variable for your input.

function getBeforePlus(str){

    return str.split("+")[0]; 
    /* This splits the string into an array using the "+" 
       character as a delimiter.
       Then it gets the first element of the split string.
    */

}

You fiddle already does the job ... maybe you try to get the string before the double colon? (you really should edit your question) Then the code would go like this:

str.substring(0, str.indexOf(":"));

Where 'str' represents the variable with your string inside.

Click here for JSFiddle Example

Javascript

var input_string = document.getElementById('my-input').innerText;
var output_element = document.getElementById('my-output');

var left_text = input_string.substring(0, input_string.indexOf(":"));

output_element.innerText = left_text;

Html

<p>
  <h5>Input:</h5>
  <strong id="my-input">Left Text:Right Text</strong>
  <h5>Output:</h5>
  <strong id="my-output">XXX</strong>
</p>

CSS

body { font-family: Calibri, sans-serif; color:#555; }
h5 { margin-bottom: 0.8em; }
strong {
  width:90%;
  padding: 0.5em 1em;
  background-color: cyan;
}
#my-output { background-color: gold; }

This is the what you should use to split:

string.slice(0, string.indexOf("'"));

And then to handle your non existant value edge case:

function split(str) {
 var i = str.indexOf("'");

 if(i > 0)
  return  str.slice(0, i);
 else
  return "";     
}

Demo on JsFiddle

You should probably split the values first using the commas and then split each value within that with the hyphen. Maybe something like this?

var firstArray[];
var secondArray[];
var strArray[] = str.split(",");
for (var i=0 ; i<strArray.length; i++){
   var strVal[] = strArray[i].split("-");
   firstArray.push(strVal[0]);
   secondArray.push(strVal[1]);
}

You can do this in one line using destructuring

A working example

var [before, after] = 'Username|Jackie'.split("|")

console.log(before)
console.log(after)

The above is the same as doing this:

var pieces = 'Username|Jackie'.split("|")
var before = pieces[0]
var after = pieces[1]

console.log(before)
console.log(after)

A pretty simple easy to read solution would be to split the string by T and grab the first element like this:

"2022-04-01T09:00".split("T")[0]

Other alternatives include:

• Using "2022-04-01T09:00".replace(/T.*$/, '') which will replace everything after (and including T) with an empty string.

• Grabbing the first 10 characters using "2022-04-01T09:00".substring(0, 10)

Split separates the string into tokens separated by the delimiter. It always returns an array one longer than the number of tokens in the string. If there is one delimiter, there are two tokens—one to the left and one to the right. In your case, the token to the left is the empty string, so split() returns the array ["", "mysite.com/username_here80"]. Try using

var urlsplit = url.split("mycool://?string=")[1]; // <= Note the [1]!

to retrieve the second string in the array (which is what you are interested in).

The reason you are getting a comma is that converting an array to a string (which is what alert() does) results in a comma-separated list of the array elements converted to strings.