What Is the Third Argument in JavaScript setTimeout()?

The JavaScript setTimeout() method has the following syntax:

setTimeout(function[, delay, arg1, arg2, ...]);

Starting from the (optional) third argument, you can specify an arbitrary number of arguments to the JavaScript setTimeout() method, which are all passed through to the provided timeout callback function. For example:

function timeoutFunc(...args){
    console.log(args[0], args[1], args[2]);
}

setTimeout(timeoutFunc, 500, 'foo', 'bar', 'baz'); // 'foo bar baz'

You can have many possibilities with this. For example, you could use this with a Promise to resolve with a value provided in the third argument:

const promise = new Promise((resolve, reject) => {
  setTimeout(resolve, 1000, 'foo');
});

promise.then((val) => console.log(val)); // 'foo'