why can Javascript function can update original property of object from outside but cannot update original variable

Question

    let variable1="hello";
function func1(variable){
    variable="hello hello";
}
func1(variable1);
console.log("after function: "+variable1);

let object1={
    property1:"hello2"
}
function func2(obj){
    obj.property="hello object";
}
func2(object1);
console.log("after function:" +object1.property);

I have this code, the first console.log() returns

hello

but second console.log() returns

hello object

So I understood javascript cannot change and update variable but it can change and update property of object. But why and how?