sessionStorage setItem returns true or false

Question

I'm trying to figure out what the setItem method from sessionStorage returns. As far as I could get, the following code returns undefined:

var set = sessionStorage.setItem('foo', 'bar');
console.log(set);

I need to know if the item was successfully set or if it failed. How can I accomplish this without knowing the return?

Answer 1

Take a look at the sessionStorage specification.

This line:

setter creator void setItem(DOMString key, DOMString value);

Tells us setItem doesn't return anything. (void is the return value, there)

---

You can check if the item was set like this:

if (sessionStorage.getItem('myValue') == null){
    // myValue was not set
}else{
    // myValue was set
}

Answer 2

Here is a guide on sessionStorage from the Mozilla Developer Network. It appears that sessionStorage.setItem(name, value) does not return anything.

However, if you manually wanted to check, you could try something like this:

sessionStorage.setItem('make', 'Ford');

/* Returns null if it cannot find the item in sessionStorage. */
if(sessionStorage.getItem('make')) {
    /* Session storage set successfully. */
} else {
    /* Session storage did not set successfully. */
}

Answer 3

Use try catch expression, since the method throws an exception if the session is full, as stated in the specification :

try { sessionStorage.setItem('foo', 'bar'); }
catch(oops) {
     // maybe no more space, try to free
     localStorage.removeItem('foo');
     sessionStorage.setItem('foo', 'bar');
}