Turn a JavaScript local variable into a global variable

Declare the variable outside the scope of the function:

var foo = null;

function myClickEvent() {
    foo = someStuffThatGetsValue;
}

Better yet, use a single global variable as the namespace ("MyApp") for your application, and store the value inside that:

var MyApp = {
    foo: null
};

function myClickEvent() {
    MyApp.foo = someStuffThatGetsValue;
}

The function itself could even be included in there.

You should be able to add the variable's value to a property of the global window object:

window.yourVarName = yourVarName;

Then the other functions will be able to access yourVarName simply by referencing yourVarname directly. There will be no need to use window.yourVarName.

However keep in mind that in general, global variables are evil.