Truthy

Truthy is a term used in web development to describe a value that is considered true when evaluated in a boolean context. A boolean context is any situation where a value is evaluated as either true or false, such as in a conditional statement, a loop, or a function that expects a boolean value. In JavaScript, truthy values are any values that are not explicitly false, including empty strings, zero, null, undefined, and NaN. Understanding truthy values is important for writing efficient and bug-free code, as well as for avoiding common programming mistakes.

Usage

In web development, truthy values are used in a variety of contexts to determine whether a value should be considered true or false. For example, in a conditional statement, the condition will be evaluated as true if the value is truthy, and false if the value is falsy. This can be useful for branching logic in an application, such as redirecting a user to a different page based on their input.

// Example of using truthy values in a conditional statement
if (userInput) {
  // do something if userInput is truthy
} else {
  // do something else if userInput is falsy
}

Truthy values are also commonly used in loops, such as while loops or for loops, to determine when the loop should continue or end. In this context, a truthy value will cause the loop to continue, while a falsy value will cause the loop to end.

// Example of using truthy values in a while loop
let i = 0;
while (i < 10) {
  // do something while i is less than 10
  i++;
}

Another common use of truthy values is in functions that expect a boolean argument. For example, a function that toggles a button might expect a boolean value to determine whether the button is currently active or inactive. In this case, a truthy value would represent an active button, while a falsy value would represent an inactive button.

// Example of using truthy values in a function
function toggleButton(isActive) {
  if (isActive) {
    // set button to inactive
  } else {
    // set button to active
  }
}

In addition to these common use cases, truthy values can also be used in more advanced programming techniques, such as short-circuit evaluation, which allows for more concise and efficient code.

// Example of using truthy values in short-circuit evaluation
let value = x || y;

In this example, the value of value will be set to x if x is truthy, and y if x is falsy. This technique can be useful for avoiding unnecessary computation or for providing default values.

Examples

To better understand truthy values, let’s take a look at some examples.

If we have a variable x with the value of 0, we can test if it is truthy or falsy by evaluating it in a boolean context:

// Example of testing a variable for truthiness
if (x) {
  console.log("x is truthy");
} else {
  console.log("x is falsy");
}

In this case, the output would be "x is falsy", because 0 is considered falsy in JavaScript.

However, if we have a variable y with the value of "hello", it would be considered truthy:

// Example of testing a variable for truthiness
if (y) {
  console.log("y is truthy");
} else {
  console.log("y is falsy");
}

In this case, the output would be "y is truthy", because "hello" is considered truthy in JavaScript.

One important thing to note about truthy values is that they are not always equivalent to the boolean value true. This means that a truthy value may not always be identical to true when compared using the == or === operators.

For example, if we compare x to false, it will return true, even though x is considered falsy:

// Example of comparing a variable to false
if (x == false) {
  console.log("x is falsey");
} else {
  console.log("x is not falsey");
}

In this case, the output would be "x is falsey", because 0 is considered falsy and is equivalent to false when compared using the == operator.

However, if we compare y to true, it will return false, even though y is considered truthy:

// Example of comparing a variable to true
if (y === true) {
  console.log("y is true");
} else {
  console.log("y is not true");
}

In this case, the output would be "y is not true", because "hello" is considered truthy but is not identical to true when compared using the === operator.

Understanding these nuances of truthy values is important for writing clear and accurate code, as well as for avoiding common programming mistakes.