Your function's code is fine.

However, you are logging the array using console.log before func1() gets to run, since window.onload fires AFTER everything has loaded.

Let's focus on why the console.log in the end is empty.

Note that :

window. onload() is invoked when all resources (the document, objects, images, css, etc) have finished rendering.

So after the console output the list value, if will execute the func1 and assign the value to list, but before that list is just an empty array.

If could see the following snippet, if you put the console to the window.onload function, it works as epected.

You could use push to add item to array and use index to access a specific element.

window.onload = function(){
    func1();
    console.log(list);
    func2()
    console.log(list)
};

var list = [];

function func1(){
  for(var i = 0; i < 9; i++){
    list.push(i);
  }
}
console.log(list);
function func2(){
list[0] =9999

}

You need to wait for the window to load and call your function func1 before logging the value of the array to console...

window.onload = function(){
    func1();
    console.log(list);
};

var list = [];

function func1(){
  for(var i = 0; i < 9; i++){
    list.push(i);
  }
}