Context in JavaScript closures

Closures are functions which use variables from the surrounded context. Using them without think about can result in unpredictable side effects:

var context = 'a';
var closure = function () {
    console.log(context);
};
closure(); // console.log: a
context = 'b';
closure(); // console.log: b

The closure use and depends on the current values of the context variables. The same function call with the same arguments results in different behaviors.

A possible way to save the state of the context is to wrap the closure with a self calling function:

var context = 'a';
var closure = function (context) {
  return function () { console.log(context) };
}(context);
closure(); // console.log: a
context = 'b';
closure(); // console.log: a

The value of the argument get copied into the parameter which no longer changes and every function call results in the same behavior.

Summary

Closures are useful and flexible. But care about using them with mutable context variables.