What does || mean in JavaScript?

Question

I'm fairly new to JavaScript. What does || do?

Answer 1

It is a condition operator, meaning “or”, typically used like this:

if (browserIsMSIE || browserIsFirefox) {
  …
}

Answer 2

MDN Expressions and Logical statements

(Logical OR) Returns expr1 if it can be converted to true; otherwise, returns expr2. Thus, when used with Boolean values, || returns true if either operand is true; if both are false, returns false.

var o1 =  true || true;     // t || t returns true
var o2 = false || true;     // f || t returns true
var o3 =  true || false;    // t || f returns true
var o4 = false || (3 == 4); // f || f returns false
var o5 = "Cat" || "Dog";    // t || t returns Cat
var o6 = false || "Cat";    // f || t returns Cat
var o7 = "Cat" || false;    // t || f returns Cat

Answer 3

If something1 or something2, do something: equates to this

if (something1 || something2){
    ... do something
}

If something1 and something2, do something: equates to this

if (something1 && something2){
    ... do something
}

Answer 4

It's same as in other C type languages. A Logical Operator, for the OR condition.

Here's the Docs on Mozilla Developer Network.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators