Filterring an Array of Objects

You are using filter, like it filters out elements, while it actually keeps elements that fit the condition. Change your condition to e.id !== 2 and it keeps all elements with ids not equal to 2:

var list = new Array();
list.push({name: 'apple', id: 1})
list.push({name: 'bread', id: 2})
list.push({name: 'milk', id: 3})
list.push({name: 'butter', id: 4})

console.log(list.filter(e => e.id !== 2));

.as-console-wrapper { max-height: 100% !important; top: 0; }

You need to invert the logic of the filter predicate function.

list.filter(e => e.id !== 2);

filter returns only the items that match the predicate - in your case it will return a list of only one element which has the ID of 2.

Testing with indexOf you're searching for an array with the element that you've found.

filter returns an array with the results. You should use find instead which returns a single element:

var list = new Array();
list.push({name: 'apple', id: 1})
list.push({name: 'bread', id: 2})

var index = list.indexOf(list.find(e => e.id === 2));
var result = index !== -1;

console.log('index', index);
console.log('result', result);

When you use list.filter(e => e.name === 2). It will return an array include the object , not the object itself. So it will return -1. You can use the spread syntax to extract the object out of the array contain it:

list.indexOf(...list.filter(e => e.id === 2))

indexOf won't work as you will be searching for an object and object comparison in JavaScript is tricky (a custom evaluater is needed to check sameness). The good news is you may not need it.

As noted in comments and elsewhere, filter was behaving opposite to what you desired. Changing the comparison operator from === to !== is one way to solve that issue.

In the code below, I've included some other goodies you may find value, such as:

• the Array.of()
• shorthand property names (e.g., { foo } === {'foo': foo})
• series execution using the comma operator (i.e. ,) especially to avoid curly-braces
• ... as a rest operator for function arguments
• and others

let search_id = 2;             // id to filter out

let list = Array.of(
 {name: 'apple',  id: 1},
 {name: 'bread',  id: 2},
 {name: 'orange', id: 3},
 {name: 'bagel',  id: 4}
)
log({list});


let filtered = list.filter(e => e.id !== search_id)
log({filtered});


if (filtered.length)
  log(`Found ${filtered.length} matches!`);
else
  log(`The id of ${search_id} has not been found`);




// Simple logger so label is on its own line
function log(){
  let [param1,...args]=arguments;
  
  switch (typeof param1){
    case 'string': 
      if (args.length)
        console.log(`${param1}:`),  // comma intentional
        console.log(args.pop())
      else
        console.log(param1);
      break;
    case 'object':
      for (let key in param1)
        console.log(`${key}:`),   // comma intentional
        console.log(param1[key])
      break;
    default:
      console.log('Error in passed arguments.  Type not recognized.')
  }      
}