javascript: Save functions with variable arguments in an array

Question

This might have been asked several times, but I don't find it. The following code does - of course - not what it obviously intends:

var arr = [];
var count = 10;

var funct = function() { console.log("count when called: ", count); };


while (count--) {

  arr.push(funct);
}


for (i in arr) {
  arr[i]();
}

I got logged -1 in each for loop, because the function accesses the count value of the environment in which it was created. and count has the -1 value after the while loop.

What I need is something like passing an argument to the creation of the function. Any hints?

Like this -> jsfiddle.net/adeneo/dqnthjf0

adeneo
– adeneo

2015-05-24 13:33:13 +00:00
Commented May 24, 2015 at 13:33 — adeneo
– adeneo, Commented May 24, 2015 at 13:33

Shomz · Accepted Answer · 2015-05-24 13:35:51Z

1

Your function needs to have a parameter, and then return a function that will make use of that parameter so it can be executed later. Something like this should work:

var arr = [];
var count = 10;

var funct = function(c) { 
  return function() {console.log("count when called: ", c);} 
};


while (count--) {
  arr.push( funct(count) );
}


for (i in arr) {
  arr[i]();
}

answered May 24, 2015 at 13:35

Shomz

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Comments

Giuseppe Pes · Accepted Answer · 2015-05-24 13:36:29Z

1

What you can do is to wrap the function funct within a second closure in order to create a local version of the variable count.

For example:

var arr = [];
var count = 10;

var funct = function () {
  var currentCount = count;
  return function() { console.log("count when called: ", currentCount); };
}


while (count--) {
  arr.push(funct());
}


for (i in arr) {
  arr[i]();
}

Output:

count when called:  9
count when called:  8
count when called:  7
count when called:  6
count when called:  5
count when called:  4
count when called:  3
count when called:  2
count when called:  1
count when called:  0

JSFIDDLE: https://jsfiddle.net/gwswjtug/

Open the console to see the results.

answered May 24, 2015 at 13:36

Giuseppe Pes

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Comments

tiblu · Accepted Answer · 2015-05-24 13:38:24Z

1

Use closures - http://www.w3schools.com/js/js_function_closures.asp

var arr = [];
var count = 10;

var funct = function(i) { 
    return function() {
        console.log("count when called: ", i); 
    }
}


while (count--) {
    arr.push(funct(count));
}


arr.forEach(function(fn) {
    fn();
});

Fiddle: http://jsfiddle.net/ort1t6e2/

answered May 24, 2015 at 13:38

tiblu

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