Remove chance of unexpected type coercion and remove unnecessary param to `TextEncoder`

[Anupya]

In this PR:

• Use === instead of == and !== instead of != as the latter may cause unexpected type coercion [source].
• TextEncoder only supports utf-8 and does not accept any input params [source]. So we should declare it like TextEncoder instead of TextEncoder('utf-8').
• Use const/let instead of var where appropriate.
• Remove stringify-object as it is unused because pretty is unused.

[niklasf]

Thanks!