JavaScript Toggle Variable
var thing = true; //try changing this to false
thing = !thing; //the variable will go from true to false, or from false to true
The Amateur
var thing = true; //try changing this to false
thing = !thing; //the variable will go from true to false, or from false to truestate.map((todo, index) => (index === action.index) ? {...todo, completed: !todo.completed} : todo)