Create a <ul> and fill it based on a passed array

I've managed to generate a series of list-items based on one specified array within a matrix (i.e. an array within an array).

I would like to be able to pass a variable (representing an array) to a function so that it can spit out an unordered list filled with list-items based on the array passed into it.

Problems:

• The function only works with one array at a time
• It also produces commas in the markup (presumably, because it's converting the array to a string)

The solution needs to:

• assume that the unordered list does not exist in the DOM
• be able to accept different arrays passed into it (options[0], options[1], etc.)
• generate the list-items without commas

JavaScript:

var options = [        set0 = ['Option 1','Option 2'],
        set1 = ['First Option','Second Option','Third Option']
    ]

function makeUL(){
    var a = '<ul>',
        b = '</ul>',
        m = [];

    // Right now, this loop only works with one
    // explicitly specified array (options[0] aka 'set0')
    for (i = 0; i < options[0].length; i += 1){
        m[i] = '<li>' + options[0][i] + '</li>';
    }

    document.getElementById('foo').innerHTML = a + m + b;
}
    
// My goal is to be able to pass a variable
// here to utilize this function with different arrays
makeUL();

jsFiddle

First of all, don't create HTML elements by string concatenation. Use DOM manipulation. It's faster, cleaner, and less error-prone. This alone solves one of your problems. Then, just let it accept any array as an argument:

var options = [        set0 = ['Option 1','Option 2'],
        set1 = ['First Option','Second Option','Third Option']
    ];

function makeUL(array) {
    // Create the list element:
    var list = document.createElement('ul');

    for (var i = 0; i < array.length; i++) {
        // Create the list item:
        var item = document.createElement('li');

        // Set its contents:
        item.appendChild(document.createTextNode(array[i]));

        // Add it to the list:
        list.appendChild(item);
    }

    // Finally, return the constructed list:
    return list;
}

// Add the contents of options[0] to #foo:
document.getElementById('foo').appendChild(makeUL(options[0]));

Here's a demo. You might also want to note that set0 and set1 are leaking into the global scope; if you meant to create a sort of associative array, you should use an object:

var options = {
    set0: ['Option 1', 'Option 2'],
    set1: ['First Option', 'Second Option', 'Third Option']
};

And access them like so:

makeUL(options.set0);

What are disadvantages of the following solution? Seems to be faster and shorter.

var options = {
    set0: ['Option 1','Option 2'],
    set1: ['First Option','Second Option','Third Option']
};

var list = "<li>" + options.set0.join("</li><li>") + "</li>";
document.getElementById("list").innerHTML = list;

You may also consider the following solution:

let sum = options.set0.concat(options.set1);
const codeHTML = '<ol>' + sum.reduce((html, item) => {
    return html + "<li>" + item + "</li>";
        }, "") + '</ol>';
document.querySelector("#list").innerHTML = codeHTML;