HTML5 LocalStorage Checking if a key exists

Question

Why this does not work     if typeof localStorage getItem  username      undefined        alert  no         The goal is to redirect the user from the index page to the login page if not already logged  Here the localStorage getItem  username    variable is not defined for the moment   It s for an ios phonegap app

User · Accepted Answer

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

User · Answer

Update   if  localStorage hasOwnProperty  username                 Another way  relevant when value is not expected to be empty string  null or any other falsy value   if  localStorage  username

User · Answer

This method worked for me   if   username  in localStorage        alert  yes      else       alert  no

User · Answer

The MDN documentation shows how the getItem method is implementated   Object defineProperty oStorage   getItem           value  function  sKey    return sKey   this sKey    null           writable  false        configurable  false        enumerable  false           If the value isn t set  it returns null  You are testing to see if it is undefined  Check to see if it is null instead   if localStorage getItem  username       null

[javascript] HTML5 LocalStorage: Checking if a key exists

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