Checking a variable is undefined with typeof

Remember that typeof returns a string, meaning this will work: typeof variable === 'undefined'

but this will not: typeof variable === undefined

Omitting the typeof will trigger an error directly, as you're acting on an undefined variable.

Relatedly, the following will check if a variable is undefined or null:

if (myVar == null) {
  // true if myVar is null or undefined
}

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