What is a “closure”?

A closure is the combination of a function enclosed with references to its surrounding state (lexical environment). It gives you access to an outer function’s scope or environment from an inner function.

Consider the following code snippet:

function outerFunction() {
  let innerVar = "I'm inside outerFunction"
  function innerFunction() {
    console.log(`${innerVar}, but I can be accessed from innerFunction too!`)
  }
  innerFunction()
}

outerFunction()

// > "I'm inside outerFunction, but I can be accessed from innerFunction too!"

Lexical Scope/Environment

In the above code snippet, outerFunction creates a variable called innerVar, and a function called innerFunction. The innerFunction function is enclosed inside, and is only available within, outerFunction. innerFunction has no local variables of its own, but is able to access innerVar because they are both within the lexical scope of outerFunction.

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