How much junk you got in localStorage? Useful for figuring out how close you're getting to the localStorage cap.

localstorage-size.js

/**
 * Return total byte size of all current keys in localStorage.  Based on
 * UTF-8 encoding for byte size, so not guaranteed to be accurate in 
 * other encodings.
 */
localStorage.__proto__.size = function () {
  return Object.keys( this )
    .map( function ( key ) {
      return ( new TextEncoder( 'utf-8' ).encode( localStorage[ key ] ) ).length;
    })
    .reduce( function ( length, next ) {
      return length + next;
    }, 0 );
};