javascript localstorage check if item exists code example

Example 1: javascript check if variable exists

if (typeof myVar !== 'undefined') {
    // myVar is defined
}

Example 2: check if localstorage key exists

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

Example 3: check if localstorage key exists js

if("user" in localStorage){
   alert('yes');
} else {
   alert('no');
}