How to check if local storage key does not exist?

Question

I can find if the local storage key exists or not using the if condition in the below code

    this.data = localStorage.getItem('education'); 
      if(this.data)//check if it exists or not empty
{
        console.log("Exists");
      }

If want to use if condition to find if it does not exist, how do I write that in code? I don't want to use else.

You mean by negating the condition in the code? `if (!(this.data)) { console.log("DOH!"); }` — Matteo Ragni, Sep 03 '17 at 10:56
I'm sorry but does not exist something like "accepting the question". Questions can be only upvoted or downvoted. — Matteo Ragni, Sep 03 '17 at 11:38
Possible duplicate of [How to check if value exist in Local Storage data set?](https://stackoverflow.com/questions/47167393/how-to-check-if-value-exist-in-local-storage-data-set) — Nikola Lukic, Jun 01 '19 at 22:51

Matteo Ragni · Accepted Answer · 2018-09-14T13:36:29.027

2

If this.data is undefined, than !(this.data) should work:

if (!(this.data)) { console.log("DOH!"); }

Edit: I just received a comment that raises a point. What if the key is false? It is not enough. What if the key actually exists and it is set to undefined? Then the method will fail. Thus probably it is better to use the in keyword (as described in this answer)

if (!("data" in this)) { console.log("DOH!"); }

as for example:

obj = { a: false, b: undefined }
if (!("a" in obj)) { console.log("a does not exist"); }
if (!("b" in obj)) { console.log("b does not exist"); }
if (!("c" in obj)) { console.log("c does not exist"); }

The output is

c does not exist

edited Sep 14 '18 at 13:36

answered Sep 03 '17 at 11:27

Matteo Ragni

2,837
1
20
34

This will fail if the value is false and you want to set it to "true" by default. Better to check if this.data is undefined and then act. – José Manuel Blasco Sep 14 '18 at 10:49
1

you're right. I fixed it. It is still bad idea to check if it is undefined. What if a key is undefined then? – Matteo Ragni Sep 14 '18 at 13:36
You're right too :) For my example I wanted the value to start to "true" if it wasn't setted. But your example covers all the scenarios. Good work – José Manuel Blasco Sep 17 '18 at 06:48

How to check if local storage key does not exist?

1 Answers1