Variable value changes

Suppose we have a variable to which we have assigned some value. We can apply again the assignment operation then and assign an another value to this variable:

javascriptlet a;    // declare a variable

a = 1;    // assign the value 1 to it 
alert(a); // shows 1

a = 2;    // now assign the value 2, overwriting the value 1
alert(a); // shows 2

That is, the value of a variable is not something rigidly attached to it. We can freely write some data to a variable, read it, then write something else - and so on.