Checking String Equality in JavaScript: Uncover the Best Practice

When comparing strings in JavaScript, there are two operators: == and ===. Which one to use can be a source of confusion. This guide will clarify the correct way to check for string equality and delve into the reasons behind it.

The Recommended Approach: Use ===

Until you thoroughly grasp the differences and implications between == and ===, it's highly advisable to use ===. This operator ensures consistency and prevents unexpected results due to the type coercion performed by ==.

The Type Equivalence Issue with ==

Using == for string comparison can lead to unexpected behavior. This is because == first checks if the values on both sides are of the same type, performing type coercion if necessary. For example:

'1' == 1 // true

In this case, == coerces '1' to a number (1) before comparing it, resulting in a true result.

False Positives with Boolean Expressions

Using == can also result in false positives when comparing strings to Boolean values:

'true' == true // true

Here, == converts 'true' to a boolean (true) before comparison.

Avoid these Pitfalls: Use ===

To avoid these type-related pitfalls, always use === for string equality checks. It performs strict comparison without type coercion, ensuring reliable results.

Exception: Partial String Matching

There may be rare cases where you intentionally want partial string matching. In these scenarios, you can use .includes() or .startsWith() methods:

'Hello World'.includes('World'); // true

Additional Resources

For further understanding, consider the following resources:

• [Mr. Douglas Crockford's Google Tech Talk](http://www.youtube.com/watch?v=hQVTIJBZook)
• [You Don't Know JS series by Kyle Simpson](https://www.udemy.com/course/the-complete-javascript-course/#/)
• [Up & Going book: Equality section](https://upgoing.org/javascript)