Question

What I want to do is to sending data between two handlers.

element.onmousedown = function() {
    data = precalculate();
}

element.onmouseup = function() {
    dosomething(data);
}

if the data is a global variable it works. People says global variable is evil. But I don’t know how to do without it.

or I misunderstood “global variable”?

Answer 1

Just scope the variable if you don’t want/need it to be global:

(function() {
    var data;
    element.onmousedown = function() {
        data = precalculate();
    }

    element.onmouseup = function() {
        dosomething(data);
    }
})();

---

EDIT: To clarify, the only way to create a new variable scope in javascript is in a function.

Any variable declared with var inside a function is inaccessible to the outer scope.

In the code above, I created an IIFE (immediately invoked function expression), which is simply a function that is invoked as soon as it is created, and I placed your data variable (along with the handler assignments) inside of it.

Because the handlers were created in a scope that has access to the data variable, they retain their access to that variable.

To give another example:

var a = "a"; // global variable

(function() {

    var b = "b";  // new variable in this scope

    (function() {

        var c = "c";  // new variable in this scope

        // in this function, you have access to 'a', 'b' and 'c'

    })();

    // in this function you have access to 'a' and 'b' variables, but not 'c'

})();

// globally, you have access to the 'a' variable, but not 'b' or 'c'