weird array behaviour in javascript

Question

I know arrays in javascript are a bit special, compared to other languages, but I don\'t really get this behaviour, or what\'s going on here.

I\'d like to know why i

Answer 1

arr is a parameter to your function already, and it is not undefined. var gets hoisted, so to the interpreter, your current code actually looks something like:

function setupWindowProgBar(settings, window, palette, arr){
  var arr; // **does not reassign the parameter**
  console.log('start');
  console.log(arr);
  if(typeof arr == 'undefined'){
    arr = [];
  }
  console.log(arr);
  console.log('stop');
}

You should never be declaring a variable whose name is already scoped to the block/function you're using it in.

If arr actually isn't defined in the argument, then it will be assigned to an array on the line arr = [];, but at least on Chrome, that empty array will not necessarily be printed at the time you console.log it.

console.log(arr); does not necessarily immediately display the arr - depending on your browser, it may only be populated in your console after you open your console, after this line has run:

arr[arr.length] = createProgBar('master', 'bg', window, ...