Is it possible to define a JavaScript global variable within a function?

General Discussions
1

Is it possible to declare a global variable in JavaScript within a function and access it in other functions? For example, if I declare and assign the trailimage variable inside the makeObj() function, can it be used in followmouse() or other functions?

2

Declare Global Variable Outside the Function In this approach, the trailimage variable is declared outside the makeObj function. The function assigns a value to this global variable.

var offsetfrommouse = [10, -20];
var displayduration = 0;
var obj_selected = 0;
var trailimage; // Declare the global variable here
function makeObj(address) {
trailimage = [address, 50, 50]; // Assign value to the global variable
document.write('<img id="trailimageid" src="' + trailimage[0] + '" border="0" style="position: absolute; visibility:visible; left: 0px; top: 0px; width: ' + trailimage[1] + 'px; height: ' + trailimage[2] + 'px">');
obj_selected = 1;
}
3

Another way to define a JavaScript global variable within a function is to explicitly attach the variable to the window object, which is the global scope in browsers.

var offsetfrommouse = [10, -20];
var displayduration = 0;
var obj_selected = 0;
function makeObj(address) {
window.trailimage = [address, 50, 50]; // Assign value to the global variable using the window object
document.write('<img id="trailimageid" src="' + window.trailimage[0] + '" border="0" style="position: absolute; visibility:visible; left: 0px; top: 0px; width: ' + window.trailimage[1] + 'px; height: ' + window.trailimage[2] + 'px">');
obj_selected = 1;
}
4

You can define a JavaScript global variable by declaring it without the var, let, or const keyword inside a function. This approach automatically attaches the variable to the global scope.

var offsetfrommouse = [10, -20];
var displayduration = 0;
var obj_selected = 0;
function makeObj(address) {
trailimage = [address, 50, 50]; // Assign value to the global variable without var, let, or const
document.write('<img id="trailimageid" src="' + trailimage[0] + '" border="0" style="position: absolute; visibility:visible; left: 0px; top: 0px; width: ' + trailimage[1] + 'px; height: ' + trailimage[2] + 'px">');
obj_selected = 1;
}