A JavaScript global variable is declared outside the function or declared with window object. It can be accessed from any function.
Global variables are declared outside of a function for accessibility throughout the program, while local variables are stored within a function using var
for use only within that function’s scope. If you declare a variable without using var
, even if it’s inside a function, it will still be seen as global:
var x = 5; // global
function someThing(y) {
var z = x + y;
console.log(z);
}
function someThing(y) {
x = 5; // still global!
var z = x + y;
console.log(z);
}
function someThing(y) {
var x = 5; // local
var z = x + y;
console.log(z);
}
A global variable is also an object of the current scope, such as the browser window:
var dog = “Fluffy”;
console.log(dog); // Fluffy;
var dog = “Fluffy”;
console.log(window.dog); // Fluffy