JavaScript: Pass a variable from one function to another, using setInterval()?

Question

So I have a function that loops executing a function, example:

function(f){
  var variable;
  for(z = 0; z < 10; z++){
    variable = "cool";         
    setInterval(f)
  }

Btw, the real function is MUCH more complex than this but it's the same theory. I want to be able to execute the function in argument f and set some variables (ex. variable) so that this function can use them, in a whole this is the idea:

function say(f){
   var variable = "hey";
   setInterval(f);
}
say(function(){
   alert(variable)
});

Here, one should get an alert box saying hey. That's the theory, but it wont work:

Variable "variable" isn't defined

The browser will probably just ignore the error and alert undefined.

But anyways, how do I "pass" the variable without changing the scope of it.

Jacob Relkin · Accepted Answer · 2010-12-08 00:22:36Z

7

JavaScript has closures, so you can do this:

var x = 0;
setInterval(function() {
   //do something with x
}, 1000);

In your specific case, you should do this:

function say(f){
   var variable = "hey";
   setInterval(function() { 
       f(variable); //invoke the say function's passed-in "f" function, passing in "hey"
   }, 1000);
}
say(function(arg){
    //arg will be "hey"
    alert(arg);
});

setInterval takes two arguments, the second being the amount of time (in milliseconds) that you wish to delay execution of the passed-in function reference.

edited Dec 8, 2010 at 0:22

answered Dec 8, 2010 at 0:17

Jacob Relkin

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1 Comment

JCOC611 Over a year ago

I know the setInterval takes two arguments. Setting the second one to zero is almost the same as not setting it, it will execute in no amount of time. Just a easy way of executing things, even though there are other (probably better) ways.

William Niu · Accepted Answer · 2010-12-08 00:34:27Z

3

If you prefer to have a function without parameter, you could consider using the call or apply method:

function say(f){
   var variable = "hey";
   setInterval(function() { 
       f.call(variable); // set the context
   }, 1000);
}
say(function(){
    alert(this);
});

answered Dec 8, 2010 at 0:34

William Niu

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1 Comment

JCOC611 Over a year ago

This is, in my opinion, the BEST method, thanks! The other ones are almost the same, but this one just looks cleaner, and is exactly what I needed.

Phrogz · Accepted Answer · 2010-12-08 00:20:31Z

1

Given that the lambda function is coming from another scope, you can't use a closure to get the value in the function directly. You'll have to pass the value to your function directly via a closure, and be prepared to receive it in the lambda:

function say(f){
   var variable = "hey";
   setInterval( function(){ f(variable) }, 500 );
}
say(function(yyy){
   alert(yyy);
});

answered Dec 8, 2010 at 0:20

Phrogz

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1 Comment

JCOC611 Over a year ago

What's lambda lol, anyways, it's a good method even though I prefer not to rely on the existence of an argument at "the other side" (in this case yyy)

mhitza · Accepted Answer · 2010-12-08 01:01:13Z

1

function say(f){
  var variable = "hey";
  setInterval(function(){
    f.call(null, variable);
  }, 1000);
}
say(function(variable){
   alert(variable)
});

By using the call method on the function.

edited Dec 8, 2010 at 1:01

answered Dec 8, 2010 at 0:20

mhitza

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2 Comments

mhitza Over a year ago

Fixed it now; although does not look clean anymore.

JCOC611 Over a year ago

Wise, even though f(variable) is cleaner ;) EDIT: Even though I'll end up using the call method

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