If it is the basic JavaScript split function, look at documentation, JavaScript split() Method.

Basically, you just do this:

var array = myString.split(' -- ')

Then your two values are stored in the array - you can get the values like this:

var firstValue = array[0];
var secondValue = array[1];

You can use .split() to split a string on a specified character with the results returned as an array. So then it's just a matter of looping through the array:

// given your existing variable
// feedUpdateResponse = "div1/div2/div3/div4" as set in the
// code in the question, add this:

var a = feedUpdateResponse.split("/"),
    i;

for (i = 0; i < a.length; i++) {
    document.getElementById("updateAvailable_" + a[i]).style.visibility
                                                                 = "visible";
}

According to ECMAScript6 ES6, the clean way is destructuring arrays:

const input = 'john smith~123 Street~Apt 4~New York~NY~12345';

const [name, street, unit, city, state, zip] = input.split('~');

console.log(name); // john smith
console.log(street); // 123 Street
console.log(unit); // Apt 4
console.log(city); // New York
console.log(state); // NY
console.log(zip); // 12345

You may have extra items in the input string. In this case, you can use rest operator to get an array for the rest or just ignore them:

const input = 'john smith~123 Street~Apt 4~New York~NY~12345';

const [name, street, ...others] = input.split('~');

console.log(name); // john smith
console.log(street); // 123 Street
console.log(others); // ["Apt 4", "New York", "NY", "12345"]

I supposed a read-only reference for values and used the const declaration.

Enjoy ES6!

You can pass a regex into JavaScript's split() method. For example:

"1,2 3".split(/,| /) 
["1", "2", "3"]

Or, if you want to allow multiple separators together to act as one only:

"1, 2, , 3".split(/(?:,| )+/) 
["1", "2", "3"]

You have to use the non-capturing (?:) parenthesis, because otherwise it gets spliced back into the result. Or you can be smart like Aaron and use a character class.

Examples tested in Safari and Firefox.