Question

123

Javascript - how to start forEach loop at some index

rated 0 times [ 128] [ 5] / answers: 1 / hits: 63010 / 7 Years ago, sat, april 8, 2017, 12:00:00

I have an array with alot of items, and I am creating a list of them. I was thinking of paginating the list. I wonder how can I start a forEach or for loop at some index in an array, that would be in my example the number of items in the list on each page, so that I don't need to iterate over the whole array in each loop?

arr.forEach(function (item) {

  someFn(item);

})





for (var i = 0, len = arr.length; i < len; i++) {

  someFn(arr[i]);

}

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elishaannac

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answered 7 Years ago nikhilc · Accepted Answer

You could use a copy of the array, by using Array#slice

The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.

array.slice(10, 20).forEach(someFn); // only for functions which respects API of forEach*

* parameters for a callback

Or you can start at a given index and end at a given index.

for (var i = 10, len = Math.min(20, arr.length); i < len; i++) {

    someFn(arr[i]);

}

With

Math.min(20, arr.length)

returns a value, if the array is smaller than the given value 20. For example if the array has only index 0 ... 14, you get as result 15.