Closures are one of the most powerful features available at runtime, but they are also one of the most misunderstood. The Mozilla developer network defines closures as follows:

We understand independent (free) variables as variables that persist beyond the lexical scope from which they were created. Let's look at an example:

function makeArmy() { 
    const shooters = []; 
    for (let i = 0; i < 10; i++) { 
        const shooter = () => { // a shooter is a function 
            console.log(i); // which should display it's number 
        }; 
        shooters.push(shooter); 
    } 
    return shooters; 
}