JavaScript-空数组外部函数

Question

I try to make a simple to do list but when I put let shoppingList = []; inside addItem() function it's not working. Why this is happening?

let shoppingList = [];

function addItem() {

  let Item = document.getElementById("item").value;
  let output = document.getElementById("output");
  let html = '';

  if (shoppingList.indexOf(Item) === -1) {
    shoppingList.push(Item);
  }

  for (var x = 0; x < shoppingList.length; x++) {
    html += (x + 1) + ". " + shoppingList[x] + "<br>";
  }

  output.innerHTML = html;

}

Answer 1

If you put your shoppingList array inside the function, it will create a new copy of an array - an empty one - every time the function is called, so every time the function is called it will work with a new array.

If your array is global (defined outside of the function), as in your code sample, it keeps the added values between calls.