JAVASCRIPT

trailing comma javascript

Trailing commas (sometimes called "final commas") can be useful when adding
new elements, parameters, or properties to JavaScript code.
If you want to add a new property, you can simply add a new line without
modifying the previously last line if that line already uses a trailing comma.
This makes version-control diffs cleaner and editing code might be less
troublesome.

//For arrays
var arr = [
  1, 
  2, 
  3, 
];

arr; // [1, 2, 3]
arr.length; // 3

//For objects
var object = { 
  foo: "bar", 
  baz: "qwerty",
  age: 42,
};

trailing comma javascript

Trailing comma is allowed in an array, object and function parameters. 
Now, this isn’t huge but it’s nice if in case we forget to close off or 
rather end a comma if we’re listing a bunch of items it doesn’t matter 
if we include that final extra one.

var list = [
    "one",
    "two",
    "three",   // It is valid
];

var obj = {
    one: "1",
    two: "2",
    three: "3", //  It is valid
}

function add(
    one,
    two,
    three, // It is valid
) {}

js trailing commas

const array = [24, 34, 35, 24, , , , 45];

console.log(array);
console.log(array.length)
// Response: [ 24, 34, 35, 24, <3 empty items>, 45 ]
// 8