Catching unknown keys in lookup tables
Lookup objects can replace long if-else branches and switch statements. We can make them more resilient by checking if a value exists for a given key.
Read fire tipShort-circuiting Boolean expressions
In JavaScript, && and || “short circuit”. If the result is obvious from the left value, it doesn’t evaluate the right side because that value wouldn’t make a difference.
// This function takes a long time. We don’t want to call it unnecessarily.
const someReallyComplicatedFunction = () => {
// something that returns a Boolean value
}
// The result of `true && SOMETHING` depends on the value of SOMETHING.
// JavaScript has to call the function here.
true && someReallyComplicatedFunction() // function is run
// The result of `false && SOMETHING` can never be `true`. JavaScript skips
// the right side, because that value doesn’t matter.
false && someReallyComplicatedFunction() // function is skipped
// `||` stops as soon as one value is `true`. If the first value is already
// true, it skips the right side.
true || someReallyComplicatedFunction() // function is skipped
// If the value left of `||` is `false`, we need to check the right value.
// JavaScript has to call the function here.
false || someReallyComplicatedFunction() // function is run