CODEWITHSUNDEEP
javascript
LeLo
LeLo

Reputation: 29

What does || do in console.log() in javascript?

This is a solution for FizzBuzz (it prints the numbers 1 to 100, but prints "Fizz" for numbers that are divisible by 3, "Buzz" for numbers divisible by 5, and "FizzBuzz" for numbers divisible by both).

for (var n = 1; n <= 100; n++) {
    var output = "";
    if (n % 3 == 0)
        output += "Fizz";
    if (n % 5 == 0)
        output += "Buzz";
    console.log(output || n);
}

I don't understand how the || works in console.log(output || n);

Usually a boolean expression like that evaluates to either true or false.

Upvotes: 1

Views: 1987

Answers (3)

Rodrigo Vargas
Rodrigo Vargas

Reputation: 75

The OR operator retuns the left side if it's truthy, if it's falsy retuns the right side. Same: 

var foo = output || n;
console.log(foo);

Upvotes: 2

heartyporridge
heartyporridge

Reputation: 1201

"", the empty string, is considered a "falsy" value in JavaScript. That is, when used in an expression involving boolean operators, "" is treated as false. The MDN has a resource on falsy values in JavaScript.

For example, the code snippet if ("") console.log("Hello, World!"); will not produce any output, as the if statement evaluates its expression to be false.

In the case of your solution to FizzBuzz, should output never have anything appended to it, the expression output || n will effectively be false || n, and due to the way JavaScript evaluates boolean operators, the expression will evaluate to n.

Upvotes: 1

Kasmetski
Kasmetski

Reputation: 705

When there is no output from the if's, it's print the number (n). This is what || do here ;)

Upvotes: 0

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