filter out array with array javascript

Question

how do I filter out array of objects a, where item1 is part of array b?

a = [
{
    "item1": "apple",
    "item2": "banana"
},
{
    "item1": "apple",
    "item2": "cherry"
},
{
    "item1": "melon",
    "item2": "cherry"
},
{
    "item1": "banana",
    "item2": "melon"
}]



b = [ "apple", "banana"]

the expected array would be:

expected_array = [{
                     "item": "melon",
                     "item2": "cherry"
                  }]

I tried with:

a.filter(el => !b.includes(el.item1))

but the resulting array has the same length as the original.

I am doing this in Node Red where this is my test setup:

[{"id":"ab67374c.c64458","type":"debug","z":"42edc0b9.7ba91","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":2040,"y":300,"wires":[]},{"id":"3fbdbc18.951c94","type":"function","z":"42edc0b9.7ba91","name":"cycle counter","func":"\n\nmsg.payload = msg.payload.filter(el => !msg.exclude.includes(el.altname));\n\nnode.warn(msg.payload);\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":1810,"y":320,"wires":[["ab67374c.c64458"]]},{"id":"b4b2e91f.8e4368","type":"inject","z":"42edc0b9.7ba91","name":"","props":[{"p":"payload"},{"p":"exclude","v":"[[\"melon\"],[\"banana\"]]","vt":"json"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[{\"altname\":\"melon\"},{\"altname\":\"cherry\"},{\"altname\":\"banana\"}]","payloadType":"json","x":1650,"y":320,"wires":[["3fbdbc18.951c94"]]}]

Answer 1

As others have said in comments, your code is fine but you need to assign the filter function's output to a variable.

let a = [{
    "item1": "apple",
    "item2": "banana"
  },
  {
    "item1": "apple",
    "item2": "cherry"
  },
  {
    "item1": "melon",
    "item2": "cherry"
  },
  {
    "item1": "banana",
    "item2": "melon"
  }
];
let b = ["apple", "banana"];

// assign filter output to variable `c`
let c = a.filter(el => !b.includes(el.item1));

console.log(c); // your output