What is the purpose of using OR operation on a varible with empty array?

Question

I found that implementation on a google analytics script in one of my project pages.

I was wondering what is the purpose of first line : "myArray || [] "" ?

Why to use OR operation on an array with another empty array?

  var myArray = myArray || [];
  myArray.push(['_setAccount', 'UA-39103830-1']);
  myArray.push(['_trackPageview']);

Or on any other kind of object,does not have to be array. Why to OR it with another empty array? — Nick W, Sep 20 '16 at 08:51

AhmadWabbi · Accepted Answer · 2016-09-20T09:00:13.810

0

This "or" operation assigns an empty array to myArray if it does not exist. The code above is functionally equivalent to:

if(myArray == null || myArray==undefined)
    myArray = [];
myArray.push(['_setAccount', 'UA-39103830-1']);
myArray.push(['_trackPageview']);

edited Sep 20 '16 at 09:00

answered Sep 20 '16 at 08:51

AhmadWabbi

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FYI its actually more like `if(myArray == null || myArray == undefined || myArray == 0) // or any other falsey value` – Jamiec Sep 20 '16 at 08:58
Yeah sure. I modified a little bit the answer. – AhmadWabbi Sep 20 '16 at 09:01
This example helped me to get main idea,thanks – Nick W Sep 22 '16 at 08:38

n1ru4l · Answer 2 · 2020-04-13T12:47:34.193

If you observe the below snippet, it checks for falsy values such as undefined null, 0, -0, 0n, "" and NaN (but also empty arrays []) it will assign the right if so.

var arr; // undefined
var arr = arr || [];
console.log(arr) // Output: []

var arr = null; // null
var arr = arr || [];
console.log(arr) // Output: []

var arr = ""; // empty string
var arr = arr || [];
console.log(arr) // Output: []

var arr = "Mr.7"; // string
var arr = arr || [];
console.log(arr) // Output: Mr.7

What is the purpose of using OR operation on a varible with empty array?

2 Answers2