Question 199975 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – The result of using the closure function

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It looks like you are calling a function and storing the call to that function in a variable.
Why are the outcome different?????

I thought the results would be the same, why are they different?

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5

Answers


  1. 0

    createCount() returns function and count() returns value because count is a function that is returned by createCount().

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  2. 0

    Remember that createCount returns a function object. So this:

    console.log(createCount())

    Just prints the function object. It does not CALL the function that was returned. Where as this:

    count = createCount()
console.log(count())

    Stores the function object, and then CALLS that function object. Two very different operations.

    It’s like the difference between these two:

    console.log(Math.random);
console.log(Math.random());
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  3. 0

    I’ll give you some code that makes intuitive sense.

    The code above is like

    console.log(function() {
    return a += 1 // a = 0 at first
}())

    The code below is like

    console.log(function() {
    let a = 0
    return function() {
       return a += 1
    }
}())
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  4. 0

    As you indicate this is an example of closures where a function has access to values in the outer scope, as long as they aren’t shaded by other functions.

    I think this example is a lot simpler to get a first understanding:

    function fullName(name){
  const surname = "aerial";
  return (name) => `${name} ${surname}`
}

    So surname is already replaced.

    You could also use other variables form the outer scope like process.env.SURNAME in a NodeJS process.

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  5. 0

    Look at this code…

    function createCount() 
  {
  let a = 0;
  return function (txt)
    {
    return `${txt} -> ${++a}`
    }
  }  
const 
  countA = createCount()
, countB = createCount()
  ;
console.log( countA('A') );
console.log( countA('A') );
console.log( countA('A') );
console.log( '------' );
console.log( countB('B') );
console.log( countB('B') );
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