Use of || {} in Javascript [duplicate]

Question

I saw something like this in Javascript :

   function name (secret) {
          secret = secret || {};

i can't find anywhere what exactly means secret = secret || {};

Is that mean create global variable with value of passed argument or an object?

When do you use it? When there is no argument passed?

Answer 1

What it means

If the variable secret is falsy (one of the following):

• false
• 0
• '' (empty string)
• null
• undefined
• NaN

..then set it to {} (an empty object - it's the same as new Object()).

---

Alternative code

It could also be written as this:

if (!secret) secret = {};

But as it's longer most people prefer the above.

---

Why?

This solution is useful as javascript has no default function parameters.

For example an example in PHP could look like this:

<?php
    function foo($bar = 'default') {
        echo $bar;
    }
?>

and in JS that could be

function foo(bar) {
    bar = bar || 'default';
    console.log(bar);
}
foo(); //default
foo(NaN); //default
foo(undefined); //default
foo(null); //default
foo(false); //default
foo(0); //default
foo(''); //default
foo('something'); //something
foo(12); //12
foo(1.2); //1.2

---

What if I only want to set a default if nothing else has been set?

If you only want to check for no value (no falsy values), then you can use the typeof function in JS:

function foo(bar) {
    if (typeof bar == 'undefined') bar = 'default';
    console.log(bar);
}
foo(); //default
foo(undefined); //default
foo(NaN); //NaN
foo(null); //null
foo(false); //false
foo(0); //0
foo(''); //(empty string)
foo('something'); //something
foo(12); //12
foo(1.2); //1.2