How do you create self string using special characters?

The self string can be formed with the combination of []()!+ characters. You need to remember the below conventions to achieve this pattern.

1. Since Arrays are truthful values, negating the arrays will produce false: ![] === false
2. As per JavaScript coercion rules, the addition of arrays together will toString them: [] + [] === ""
3. Prepend an array with + operator will convert an array to false, the negation will make it true and finally converting the result will produce value '1': +(!(+[])) === 1

By applying the above rules, we can derive below conditions

      (![] + [] === "false" + !+[]) === 1;
      

Now the character pattern would be created as below,

            s               e               l               f
       ^^^^^^^^^^^^^   ^^^^^^^^^^^^^   ^^^^^^^^^^^^^   ^^^^^^^^^^^^^

       (![] + [])[3] + (![] + [])[4] + (![] + [])[2] + (![] + [])[0]
       ^^^^^^^^^^^^^   ^^^^^^^^^^^^^   ^^^^^^^^^^^^^   ^^^^^^^^^^^^^
      (![] + [])[+!+[]+!+[]+!+[]] +
      (![] + [])[+!+[]+!+[]+!+[]+!+[]] +
      (![] + [])[+!+[]+!+[]] +
      (![] + [])[+[]]
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      (![]+[])[+!+[]+!+[]+!+[]]+(![]+[])[+!+[]+!+[]+!+[]+!+[]]+(![]+[])[+!+[]+!+[]]+(![]+[])[+[]]