Using triple equals (===) for comparison is a best practice

Double Equals (==)

When you use double equals, JavaScript performs a loose comparison. This means it will attempt to convert the values being compared to a common type before making the comparison.

// Example 1: Double equals with different types
console.log(5 == "5"); // true
console.log(null == undefined); // true

In the above examples, JavaScript converts the string "5" to a number (5) before comparing it to the number 5, resulting in a true comparison. Similarly, null and undefined are considered equal when using double equals.

Triple Equals (===)

When you use triple equals, JavaScript performs a strict comparison. This means it will only return true if the values being compared are of the same type and have the same value.

// Example 2: Triple equals with different types
console.log(5 === "5"); // false
console.log(null === undefined); // false

In the above examples, JavaScript does not perform any type conversions, so the comparisons return false.

Why use triple equals?

Using triple equals helps prevent unexpected behavior in your code. For example, if you're checking if a variable is null or undefined, using double equals can lead to incorrect results:

// Example 3: Incorrect result with double equals
let name = null;
if (name == undefined) {
  console.log("Name is undefined or null");
}

In this example, the condition will be true even though name is null, not undefined. Using triple equals maintain that the condition is only true if name is actually undefined:

// Example 4: Correct result with triple equals
let name = null;
if (name === undefined) {
  console.log("Name is undefined");
} else {
  console.log("Name is not undefined");
}

In summary, using triple equals (===) for comparison is a best practice in JavaScript because it maintains strict comparisons and prevents unexpected behavior.