Is the array index a string or a number?

Why is it that when looping over the indexes of an array they appear as strings, even though using a string to index an array is not allowed? Isn't this inconsistency puzzling?

for (const i in ["a", "b", "c"]) {
  console.log(typeof i + " " + i + " " + arr[i]);  // -> string 0 'a', etc.
}
arr['0'] // ERROR ts7105: Element implicitly has an 'any' type because index expression is not of type 'number':

Answer №1

Using the for ... in statement will iterate through the keys of the specified object.

When dealing with an array, the indices serve as keys. For example, calling Object.keys([4, 5, 1]) will output

["0", "1", "2"]
. To iterate over a typed array, it is recommended to use for ... of. For further information, refer to the documentation. If you require the index, consider using a standard for(let i=0;i<arr.length;i++) or
for(let [i, el] of arr.entries())
loop.

In reference to your inquiry, although it may seem illogical, utilizing the loop variable for indexing allows string indices. However, keep in mind that adding 1 to the index will result in "01" since the index is interpreted as a string.

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