In JavaScript, closures are defined as inner functions that have access to variables and parameters of outer function even after the outer function has returned.
function multi(){
let factor = 10;
return multiplyByTen(num){
return num * factor;
}
}
let multipleOfTen = multi();
let result = multipleOfTen(7);
/// output ///
70
In above example multipleOfTen function has access to parent function local variable 'factor' value.