Typescript way to slice elements from array while looping over it

Question

What is the typescript way to slice elements from an array while looping over all its elements? Obviously, I want to take into account that the array is re-indexed at every splice.

As stated in this post the javascript way of doing this would be:

var i = array.length
while (i--) {
    ...
    if (...) { 
        array.splice(i, 1);
    } 
}

Unfortunately, the typescript for (let item of array) {} loops from 0 to array.length-1 instead of the other way around like the js function above. Splicing an element in this loop would result in one item being skipped.

do you have a requirement to not create a new array? The correct way (in es6) would be to filter the array, which will create a new one with the elements you want. — A. Llorente
– A. Llorente, Commented Jul 10, 2018 at 13:00
@A.Llorente The sliced array must remain the original array (in my case, it contains objects in a datastore). However, creating a local copy of the array and looping through that copy would allow me to splice the original array without side effects. — Robycool
– Robycool, Commented Jul 10, 2018 at 13:12
The question is why would you want to alter the array? You can filter the original array and return only the elements that meet your if condition. — A. Llorente
– A. Llorente, Commented Jul 10, 2018 at 13:18

A. Llorente · Accepted Answer · 2018-07-10 14:00:42Z

2

From what I understood from your answers what you need is to filter the array:

const filteredArray = array.filter(element => {
    if (yourConditionIsTrue) { // if this element should be in the filteredArray
        return true;
    } else {
        return false
    }
});

Which can be done in one line:

const filteredArray = array.filter(element => conditionIsTrue);

This way your array remains untouched and you get a new array (filteredArray) only with the elements you need, but you don't mess up with the array you are iterating.

edited Jul 10, 2018 at 14:00

answered Jul 10, 2018 at 13:21

A. Llorente

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2 Comments

Robycool Over a year ago

from the documentation it seems like I can just write: array = array.filter(element => yourCondition). Correct? You'll notice I keep the same reference which is in fact what I meant above (sorry for unclarity).

A. Llorente Over a year ago

Yes indeed you could do it in one liner, if your function returns true the element is added, if it returns false it will not, I will update my answer because it was not clear enough

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