CODEWITHSUNDEEP
javascript
Ali
Ali

Reputation: 5476

Javascript: Could not really understand the function return

It is maybe incredibly easy but I couldn't solve what was going on.


function doSomething(a)
{
   var num=10;
   return setTimeout(
   function(){ a(num); }, 1000);
}

The only thing that actually confuses me is the a(num) part. What actually it does?
Reminder: I really am asking because I'm not familiar with the javascript syntax.

Upvotes: 0

Views: 65

Answers (3)

Gabe
Gabe

Reputation: 50493

When the function doSomething() is executed it is passed the parameter a, a is also some function that is then called when setTimeout() expires after 1 second, then calling the function a() passing the argument called num

Example usage:

// call doSomething() passing the test() function as an argument
doSomething(test);


// takes a number as an argument and shows an alert with that value
function test(number)
{
   alert(number);
}

// takes a function as an argument that will perform a 1 second timeout then execute the function called a
function doSomething(a)
{
   var num=10;
   return setTimeout(
   function(){ a(num); }, 1000);
}

Upvotes: 3

micnic
micnic

Reputation: 11245

setTimeout returns a timeoutID which can be used to cancel it using clearTimeout, so if you run doSomething a lot of times you will get different integer numbers which represent different timeoutID.

In your case a must be a function so you can call it using the parameter num

Example:

function doSomethingElse (justANumber) {
    return justANumber + 1;
}

// Here you call your function
doSomething(doSomethingElse);

// or another special case
doSomething(function (justANumber) {return justANumber + 1;});

Upvotes: 0

Matti Virkkunen
Matti Virkkunen

Reputation: 65126

It calls the function referenced by the variable a, using the value referenced by the variable num as an argument.

Upvotes: 0

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