JavaScript slice没有给我正确的数组长度值

Question

Why does it say length 1 instead of 4? The following is what I'm trying to push and slice. I try and append items.image_urls and slice them into 5 each.

items.image_urls is my dictionary array.

var final_push = []
final_push.push(items.image_urls.splice(0,5))
console.log(final_push.length)## gives me 1...?

var index = 0
final_push.forEach(function(results){
   index++ ##this gives me one. I would need 1,2,3,4,5,1,2,3,4,5. Somehting along that.
}

items.image_urls looks like this: It's an iteration of arrays with image urls.

Answer 1

That seems to be a nested array. So if you would access index 0, and then work on that array like below it will probably work:

console.log(final_push[0].length); //should print 4

Answer 2

In your example items.image_urls.splice(0,5) returns an array of items removed from items.image_urls . When you call final_push.push(items.image_urls.splice(0,5)); , this whole array is pushed as one item to the final_push array, so it now looks like [["url1", "url2", "url3", "url4", "url5"]] (2-dimensional array). You can access this whole array by calling final_push[some_index] .

But what you want instead is to add every element of items.image_urls.splice(0,5) to the final_push . You can use a spread operator to achieve this:

final_push.push(...items.image_urls.splice(0,5));

Spread syntax allows an iterable such as an array expression or string to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected

This is exactly our case, because push() expects one or more arguments:

arr.push(element1[, ...[, elementN]])

And here is an example:

 let items = { image_urls: ["url1", "url2", "url3", "url4", "url5", "url6", "url7", "url8", "url9", "url10"] }; let final_push = []; final_push.push(...items.image_urls.splice(0,5)); console.log(final_push.length); console.log(JSON.stringify(final_push)); console.log(JSON.stringify(items.image_urls)); 

Note: do not confuse Array.prototype.slice() with Array.prototype.splice() - the first one returns a shallow copy of a portion of an array into a new array object while the second changes the contents of an array by removing existing elements and/or adding new elements and returns an array containing the deleted elements .

Answer 3

The author is mixing up splice and slice . Probably a typo :)

You start at the beginning (0) and then delete 5 items.