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Iterator in a loop is a 'string' instead of 'number' #39089
Description
Activity
I guess I'm probably missing some logical reason as to why an iterator is a string but it just seems odd -- When I was writing up a quick sort algorithm, I had to do
parseInt(i)in order to make the comparison operator work with the index of the item I was comparing it to. Seems like an unnecessary step.This is the way JavaScript works and Node.js can't realistically change it. You will get the same result running your code in a browser.
for...inis not recommended for Arrays generally. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in for explanation, references, and alternatives.Option 1: If you don't want to create a new data structure from the existing data, you'll have to use a vanilla
forloop (this is the simplest and fastest approach).Option 2: You can instead iterate over both the keys and values using
movies.entries()instead of justmoviesand usingfor-of. Doing so will get you a number type for the index:const movies = [ { title: 'Requiem for a Dream', duration: 128 } ] function iteratorType(array) { for (let [i, val] of array.entries()) { console.log(typeof i) } } iteratorType(movies)
This option can be handy if you also need the value.
I'm going to close this because there isn't anything we're likely to do to change this behavior. But feel free to leave additional comments/questions if we've missed something.
Thank you all for the valuable feedback!
☺️
Version: v12.16.1, v15.14.0 (tested)
Platform(s) (tested):
What steps will reproduce the bug?
Create test array and console log out the
typeofof the iterator to see the resultSample snippet:
How often does it reproduce? Is there a required condition?
Every time. Conditions: An array with at least one value.
What is the expected behavior?
The iterator should be
typeofnumber.What do you see instead?
A typeof of 'string' is returned