How can one de-reference JavaScript variables when enclosing an outer scope

Question

Ok, here's a problem script.

var links = [ 'one', 'two', 'three' ];

for( var i = 0; i < links.length; i++ ) {
    var a = document.createElement( 'div' );
    a.innerHTML = links[i];
    a.onclick = function() { alert( i ) }
    document.body.appendChild( a );
}

This script generates three divs: one, two and three, using an array.
I've set a (Dom0 for simplicity) click handler on each div which alerts the index of its position in the array. - except it doesn't! It always alerts 3, the last index of the array.
This is because the 'i' in 'alert( i )' is a live reference to the outer scope (in this case global) and its value is 3 at the end of the loop. What it needs is a way of de-referencing i within the loop.

This is one solution and I tend to use it.

var links = [ 'one', 'two', 'three' ];

for( var i = 0; i < links.length; i++ ) {
    var a = document.createElement( 'div' );
    a.innerHTML = links[i];
    a.i = i; //set a property of the current element with the current value of i
    a.onclick = function() { alert( this.i ) }
    document.body.appendChild( a );
}

Does anyone else do anything different?
Is there a really smart way of doing it?
Does anyone know how the libraries do this?

Answer 1

You need to use this little closure trick - create and execute a function that returns your event handler function.

var links = [ 'one', 'two', 'three' ];

for( var i = 0; i < links.length; i++ ) {
    var a = document.createElement( 'div' );
    a.innerHTML = links[i];
    a.onclick = (function(i) { return function() { alert( i ) } })(i);
    document.body.appendChild( a );
}