Node JS array.includes not working as expected

Question

I have the following code which should filter one dynamic array (up to 300 thousands elements) from all elements not contained in another constant array:

orders[] //  is already filled with data
let materials = [] // create empty array
for (let scheme in schemes) { // loop constant object
    materials.push(schemes[scheme].typeID) // take id and add it to materials array
}
materials = Array.from(new Set(materials)) // filter out duplicates
console.log(materials) // everything looks fine here, 83 unique ids
for (let order in orders) { // now loop the main array
    if (!materials.includes(orders[order].type_id)) { // if order's containment id is not found in materials array
        orders.splice(order,1) // remove it from array
        order -= 1 // and one step back to compensate removed index (do I need it or is it processed normally even after .splice?) 
    }
}
// and send filtered orders into browser when certain url is requested

However not all unnecessaty records are filtered out, there are lots and lots of them whose id cannot be found in materials array.

What is my mistake and where is error?

You might want to take a look at [Array.prototype.filter()](https://developer.mozilla.org/nl/docs/Web/JavaScript/Reference/Global_Objects/Array/filter) — JasonK, Mar 08 '18 at 14:52
.. and Never ever use `let scheme in schemes` to iterate over an array... — Jonas Wilms, Mar 08 '18 at 14:53
https://stackoverflow.com/questions/3010840/loop-through-an-array-in-javascript — Jonas Wilms, Mar 08 '18 at 15:01
@JonasW. seems like the wrong iteration method was the only problem in this code, everything works as it should now — Arctomachine, Mar 08 '18 at 15:13

score 0 · Accepted Answer · answered Mar 08 '18 at 15:16

0

for (let scheme in schemes)

Thats how you iterate over keys in an object. Rather iterate over the entries in an array:

for (let scheme of schemes)

Additionally you should consider using the Set for lookup as its much faster. And map and filter might be useful:

const materials = new Set(schemes.map(scheme => scheme.typeID));

orders = orders.filter(el => materials.has(el.type_id));

answered Mar 08 '18 at 15:16

Jonas Wilms

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That approach does work and it is lightning fast. 1 second against 1 minute of my original code. – Arctomachine Mar 08 '18 at 15:30
@arctomachine glad to help :) – Jonas Wilms Mar 08 '18 at 15:32

Node JS array.includes not working as expected

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