What are falsy values in JavaScript?

The falsy values in JavaScript are 0, 0n, null, undefined, false, NaN, and the empty string "". They evaluate to false when coerced by JavaScript’s typing engine into a boolean value, but they are not necessarily equal to each other.

Falsy values in JavaScript

“A falsy value is a value that is considered false when encountered in a Boolean context.” — Mozilla Developer Network

In JavaScript, there is a special list of following 7 values, which are called falsy values — they all evaluate to false in conditionals:

• the number 0. (and -0)
• the BigInt 0n
• the keyword null
• the keyword undefined
• the boolean false
• the number NaN
• the empty string >"" (equivalent to >'' or >``)

Strictly speaking, you have to “coerce” (force) a falsy value to make it false, for example by using Boolean() or the e>? ternary operator.

Of course, the idea of there being falsy values in JavaScript begs the question, what are truthy values in JavaScript?

Truthy values are going to be everything else — anything that is not falsy evaluates to true in a conditional.

Truthy values include the empty object {} and the empty array [] — since they aren’t falsy, they are truthy, by definition.

Code example of falsy values

Here is a complete list of falsy comparisons using the loose equality (==) double equals comparison operator:

Despite all being falsy, they are not all equal with the double equals ==:

1. The values null and undefined are loosely equal to each other.
2. NaN is not equal to any other value, not even itself.
3. The other falsy values (0, 0n, false, and "") are all loosely equal.

A note on strict equality

All the above falsy values would be strictly equal to only themselves using ===, with the exception of NaN, which is the only value not strictly equal to itself in JavaScript.

Here is a complete list of falsy comparisons using the strict equality (===) triple equals comparison operator:

Conclusion

Falsy values are the way that JavaScript deals with not crashing when a conditional is passed something other than a boolean value.

Other programming languages differ, but JavaScript has its certain falsy values, and everything else is going to evaluate to true in a conditional.

The 7 falsy values are: 0, 0n, null, undefined, false, NaN, and "".

The falsy values sort-of loosely equal each other with ==, at least in that 0==0n==false=="", null==undefined, and of course remembering that NaN does not equal anything, not even itself.

Now that you understand falsy statements, try them out inside of conditionals (if statements, question mark e>? conditionals, and loops) in JavaScript.

Further Reading

• The user amrish contributed a great article on falsy values to uxworks:

• Gerard Sans uses falsy with ||, &&, and ! on Sons of JavaScript:

• Philip Obosi removes all falsy values from an array at scotch.io:

• James Padolsey has a nice article about falsy values on his blog:

• The user aubsrey explains falsy values in an answer at codecademy:

Dr. Derek Austin is the author of Career Programming: How You Can Become a Successful 6-Figure Programmer in 6 Months, now available on Amazon.