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More concise explanation of closures

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Adam Brenecki 2013-08-14 17:21:44 +09:30
parent a82859f95b
commit 5f2928df6b
1 changed files with 6 additions and 11 deletions
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15
javascript.html.markdown
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@ -255,24 +255,19 @@ permanent // = 10
// One of JavaScript's most powerful features is closures. If a function is
// defined inside another function, the inner function has access to all the
// outer function's variables.
// outer function's variables, even after the outer function exits.
function sayHelloInFiveSeconds(name){
var prompt = "Hello, " + name + "!"
function inner(){
alert(prompt)
}
setTimeout(inner, 5000)
// setTimeout is asynchronous, so this function will finish without waiting
// 5 seconds. However, once the 5 seconds is up, inner will still have
// access to the value of prompt.
// setTimeout is asynchronous, so the sayHelloInFiveSeconds function will
// exit immediately, and setTimeout will call inner afterwards. However,
// because inner is "closed over" sayHelloInFiveSeconds, inner still has
// access to the 'prompt' variable when it is finally called.
}
sayHelloInFiveSeconds("Adam") // will open a popup with "Hello, Adam!" in 5s
// inner() has access to the variable "prompt" strictly because of lexical scope.
// A closure is being demonstrated because the inner() function is being executed
// at a later time, and in fact being executed "outside" the scope where it was
// declared (inside of the implementation of setTimeout()), but yet inner() STILL
// has access to the variable "prompt". It is said that inner() has a "closure"
// over the variables of sayHelloInFiveSeconds().
///////////////////////////////////
// 5. More about Objects; Constructors and Prototypes