Lodash _.isEqualWith() Method

function isGreeting(value) {
  return /^h(?:i|ello)$/.test(value);
}

function customizer(objValue, othValue) {
  if (isGreeting(objValue) && isGreeting(othValue)) {
    return true;
  }
}

var array = ["hello", "goodbye"];
var other = ["hi", "goodbye"];

_.isEqualWith(array, other, customizer);
// → true

_.isEqual(array, other);
// → false

function caseCustomizer(a, b) {
  if (typeof a === "string" && typeof b === "string") {
    return a.toLowerCase() === b.toLowerCase();
  }
}

_.isEqualWith({ name: "Ada" }, { name: "ada" }, caseCustomizer);
// → true

_.isEqual({ name: "Ada" }, { name: "ada" });
// → false

function ignoreUpdatedAt(a, b, key) {
  if (key === "updatedAt") {
    return true;
  }
}

var left = { id: 1, name: "Ada", updatedAt: "2024-01-01" };
var right = { id: 1, name: "Ada", updatedAt: "2025-06-01" };

_.isEqualWith(left, right, ignoreUpdatedAt);
// → true

_.isEqual(left, right);
// → false

function bad(a, b) {
  return typeof a === "number" && typeof b === "number" && a === b;
  // returns false for non-numbers → forces inequality!
}

function good(a, b) {
  if (typeof a === "number" && typeof b === "number") {
    return a === b;
  }
  // undefined → default deep compare
}

_.isEqualWith({ x: 1 }, { x: 1 }, bad);
// → false  (objects hit customizer first → false)

_.isEqualWith({ x: 1 }, { x: 1 }, good);
// → true

function near(a, b) {
  if (typeof a === "number" && typeof b === "number") {
    return Math.abs(a - b) < 0.01;
  }
}

_.isEqualWith({ score: 0.1 + 0.2 }, { score: 0.3 }, near);
// → true

_.isEqual({ score: 0.1 + 0.2 }, { score: 0.3 });
// → false