How to Check Whether a Storage Item Is Set

How to check whether a Storage item is set?

The getItem method in the WebStorage specification, explicitly returns null if the item does not exist:

... If the given key does not exist in the list associated with the object then this method must return null. ...

So, you can:

if (localStorage.getItem("infiniteScrollEnabled") === null) {
  //...
}

See this related question:

• Storing Objects in HTML5 localStorage

HTML5 LocalStorage: Checking if a key exists

Quoting from the specification:

The getItem(key) method must return the current value associated with the given key. If the given key does not exist in the list associated with the object then this method must return null.

You should actually check against null.

if (localStorage.getItem("username") === null) {
  //...
}

Check if exist any Key localStorage Javascript

if (Object.keys(localStorage).length === 0) {
  alert('There is no key!'); 
}

LocalStorage - check if key exists

In JavaScript you have truthy and falsey. This means that every condition converts in an condition-statement to a boolean and represents true or false.

Explenation

If localStorage.regionCode is an empty string if(localStorage.regionCode) would converts to false otherwise true.

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For more details you could read the blog post about truthy and falsey

Checking if localStorage item exists is not working

It looks like you forgot to serialize your object prior to storing in localStorage, you need to use

localStorage.setItem('localStor', JSON.stringify(yourObject));

Then this should work as expected.

Since it appears that there is a rogue item in your localStorage, you may want to reset localStorage and try again:

localStorage.clear()

How to check if localStorage value is in array?

Just use the Array.includes method instead - it's less confusing, more appropriately matches what you're looking for, and doesn't require jQuery.

if (lines.includes(curPostId)) {
  // ...

Also note that you can simplify your syntax by assigning and getting from localStorage's dot properties directly, for example:

var lines = JSON.parse(localStorage.lines || '[]');
// ... 
localStorage.saveButton = $(this).attr('id');
// ... 
localStorage.lines = JSON.stringify(lines);

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Related Topics