Is something undefined in JavaScript?

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Checking for `undefined` in JavaScript is weird (the variable can be redefined), so I made a function to do it. This stuff (and others) is also in my [JSTypes]( type-checking library.

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  1. // As a function
  2. Evan.isUndefined = function(u) {
  3. return typeof u === 'undefined';
  4. };
  6. // In an "if"
  7. if (typeof foo === 'undefined') {
  8. // ...
  9. }

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