🔥 What are falsey values in JavaScript? 10 Must-Know Questions for Junior Developers💡🚀

#javascript #interview #career #tutorial

In JavaScript, "falsy" values are values that are treated as false in Boolean contexts, such as conditional statements (if, while), logical operations (&&, ||, !), and other areas where a Boolean value is expected. There are seven falsy values in JavaScript:

false
0 and -0
"" (empty string)
null
undefined
NaN
document.all (for historical web compatibility reasons)

Any value that is not in this list is considered "truthy". Here is an example demonstrating how JavaScript treats falsy values:

const test1 = "" // empty string
const test2 = 0 // zero
const test3 = parseFloat("hi") // NaN 

if(!test1 && !test2 && !test3){
  console.log("falsy")
} // logs falsy

In this example, test1, test2, and test3 are all falsy values, so !test1 && !test2 && !test3 returns true, and 'falsy' is logged to the console Source 8.

It's important to note that while falsy values are treated as false in Boolean contexts, they are not the same as the Boolean value false. For example, if you use the strict equality operator === to compare a falsy value with false, the result will be false, because === checks both the value and the type. Here's an example:

const test1 = "" === false // test1 is false

In this case, test1 is false because the empty string "" and false are different types (String and Boolean, respectively) Source 8.

You can convert any JavaScript value to a Boolean value using the Boolean function or the !! (double NOT) operator. This will return true for truthy values and false for falsy values:

const value = ""; // a falsy value
console.log(Boolean(value)); // false
console.log(!!value); // false

const value2 = "hello"; // a truthy value
console.log(Boolean(value2)); // true
console.log(!!value2); // true

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