is()

Value equality check with semantics similar to Object.is, but treats Immutable Collections as values, equal if the second Collection includes equivalent values.

It's used throughout Immutable when checking for equality, including Map key equality and Set membership.

const { Map, is } = require('immutable')
const map1 = Map({ a: 1, b: 1, c: 1 })
const map2 = Map({ a: 1, b: 1, c: 1 })
assert.equal(map1 !== map2, true)
assert.equal(Object.is(map1, map2), false)
assert.equal(is(map1, map2), true)run it

is() compares primitive types like strings and numbers, Immutable.js collections like Map and List, but also any custom object which implements ValueObject by providing equals() and hashCode() methods.

Note: Unlike Object.is, Immutable.is assumes 0 and -0 are the same value, matching the behavior of ES6 Map key equality.