is

is(value)

try to return value's constructor
return type: Function || null || undefined

Basically "is[methods]" are matching value of type

return type: Boolean;

• is.array(value);
• is.object(value);
• is.function(value);
• is.generator(value);
• is.boolean(value);
• is.string(value);
• is.number(value);
• is.symbol(value);
• is.null(value);
• is.defined(value); is value not undefined;

Applicably "is[methods]" are useful case;

return type: Boolean;

• is.blank(value)
  If value is blank string, return true.
• is.pure(value)
  If value is Object or Array, return true.
• is.nan(value)
  If value is primitive Number but Value is NaN, return true.
• is.self(proto)
  If proto is proto.constructor.prototype, return true.
• is.valid(value)
  If value is held any value, return true.
• is.there(value)
  If Array or Object is held something, return true.
• is.held(value)(super)
  If value is instance of super, return true.
• is.iterable(value)
  If value made generator's object, return true.