What is meant by arr[arr.length]. I mean what it really means or what it really does, I cannot understand the logic of how it works. Can anybody explain?

CodePudding user response：

arr.length is the length of the array.

arr[arr.length] is accessing by index the array length (out of bounds as length starts at 1, not index 0).

example:

const test = [1,2,3]
test[test.length]
undefined
test[test.length-1]
3

CodePudding user response：

It just requests specific index of the array, Use case: Not very elegant way of adding new element to the array, like:

arr[arr.length] = newVal
arr.push(newVal)
arr = [...arr, newVal]

CodePudding user response：

arr.length means the length of the array that spans from index 0 to arr.length - 1.

For instance if you got arr = ["a", "b", "c"], arr.length is 3.

arr[0] is "a", arr[1] is "b" and arr[2] is "c".

arr[3] does not exist, yet. but if you do arr[arr.length] = "d", you obtain ["a", "b", "c", "d"].

This is an odd construction and usually, one should simply write arr.push("d").

const arr = ["a", "b", "c"];
console.log(arr.length, arr[0], arr[1], arr[2], arr[3]);
arr[arr.length] = "d";
console.log(arr);
arr.push("e");
console.log(arr);

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CodePudding user response：

This statement gets the index of the last index of the array plus one. It is used to append items to an array. Equivalent to array.push().

var fruits = ["apple", "orange", "banana", "pear"];
// appends grapes to the array
fruits[fruits.length] = "grapes";
console.log(fruits);

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For further reading, check out W3School's page on array methods.

CodePudding user response：

Actually i am studyieng javascript at the moment and i wanted to understand this code from w3school.

  let len = arr.length;
  let max = -Infinity;
  while (len--) {
    if (arr[len] > max) {
      max = arr[len];
    }
  }
  return max;
}```