Falsy and Truthy Values in TypeScript

In JavaScript, values are divided into two categories: truthy and falsy. These terms refer to how values behave when evaluated as a boolean.

This automatic conversion occurs when the value is used in a context that expects a boolean (for example, when used as a condition in an if statement, or compared with an operator).

truthy and falsy are two concepts that are widely used in JavaScript. But don’t worry, they are very easy to understand.

Falsy Values

falsy values are those that, when evaluated in a boolean context, are considered false.

There are only six values in JavaScript that are considered falsy:

1. false: The boolean value false is obviously falsy.
2. 0: The number zero is falsy.
3. "" (empty string): A string with no characters is falsy.
4. null: Represents the absence of any value and is falsy.
5. undefined: Means that a variable has been declared but not assigned, and is falsy.
6. NaN: Stands for “Not-a-Number” which is falsy (it is the result of an invalid mathematical operation)

Let’s see it with an example,

if (!0) {
    console.log("0 is a falsy value");
}

if (!null) {
    console.log("null is a falsy value");
}

Truthy Values

truthy values are those that, when evaluated in a boolean context, are considered true.

Any value that is not falsy is considered truthy. This includes practically everything else:

• Numbers other than 0: All numbers different from 0, whether positive or negative
• Non-empty strings: Any string with at least one character, including “0” or “false”
• Objects and arrays: Any object or array, even if empty
• The boolean value true: Obviously 😉

For example,

if ("hello") {
    console.log("A non-empty string is truthy");
}

if ({}) {
    console.log("An empty object is truthy");
}

Importance of Truthy and Falsy

In JavaScript (and in other languages to a lesser extent), some programmers have a habit of relying on the implicit evaluation of these properties to “simplify” the code.

For example:

let username = "John";

if (username) {
    console.log("The user has provided a name");
} else {
    console.log("The username is empty");
}

In this code,

• username is evaluated directly in the if condition.
• If username is a non-empty string (truthy), the first branch will execute.
• If it is an empty string (falsy), the second branch will execute.