What is it

The filter() method does not change the original array

• deep copy

const oldArray = [
  {
    "name": "Raj",
    "age":"15",
    "RollNumber": "123",
    "Marks": "99", 
  }, 
  {
    "name": "Aman",
    "age":"14",
    "RollNumber": "223",
    "Marks": "69",   
  },
];

const newArray = oldArray.filter(el => el.age >= 15);

console.log(newArray); 
// [{ name: 'Raj', Age: '15', RollNumber: '123', Marks: '99' }]

console.log(oldArray);
// same as before applying filter

Chaining multiple filter conditions at once

const filteredResult = arrData.filter(
  x => x.price <= 1000 && 
  x.sqft >= 500 && 
  x.num_of_beds >=2 && 
  x.num_of_baths >= 2.5
);

Using predefined Boolean expression in filter

Predefining the callback functions to a boolean-resulting variable, filtering chain becomes more legible

// original array
const input = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

// boolean output function
const isEven = (value) => value % 2 === 0; 

const isOdd = (value) => !isEven(value);

const isPrime = (value) => {
  for (let i = 2, s = Math.sqrt(value); i <= s; i++) {
    if (value % i === 0) return false;
  }
  return value > 1;
};

// filters using expression
const even = input.filter(isEven);
const odd = input.filter(isOdd);
const prime = input.filter(isPrime);

console.log({ input, even, odd, prime });
/*
  input: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
  even: [2, 4, 6, 8, 10],
  odd: [1, 3, 5, 7, 9],
  prime: [2, 3, 5, 7],
*/