Return last index of Array

Question

I have the following code that will bring me an undetermined list; for example 5 items. I would like to return only the last item from the list.

for(var i = 0; i < data.list.length; i++){

      if(Date.parse(data.list[i].date) >= dateA){
          console.log(data.list[i].date);

      }

Answer 1

Given that the array starts at 0, you just have to access the position related to the size of the array minus one:

const valores = [1, 2, 3, 4, 5];

console.log("O último valor é:", valores[valores.length - 1]);

This way you do not depend on third party libraries and do not modify the array original, always accessing the last value with a time O(1), that is, constant regardless of the size of the array.

Answer 2

Seeing that his list is an array, you don’t even need to loop for to return the last item, just use the method reverse() and take the first index [0]:

var data = {
   list: [
      {
         date: "2018/01/10"
      },
      {
         date: "2018/01/09"
      },
      {
         date: "2018/05/01"
      }
   ]
}

console.log(data.list.reverse()[0].date); // retorna o último valor: 2018/05/01

Can use .pop() also:

var data = {
   list: [
      {
         date: "2018/01/10"
      },
      {
         date: "2018/01/09"
      },
      {
         date: "2018/05/01"
      }
   ]
}

console.log(data.list.pop().date); // retorna o último valor: 2018/05/01

Note: the problem is that the .pop() will also remove the last item from the array. So do not use it if you want to maintain the integrity of the array.

Answer 3

You can use _.last as explained here:

data = [1,2,3]
last = _.last(data)
alert(last)