Coffeescript and variable check

Question

I have the following code:

if variablename?
   alert "YES!"

l = []

if l[3]?
  alert "YES!"

It's translated into this:

var l;

if (typeof variablename !== "undefined" && variablename !== null) {
  alert("YESSS!");
}

l = [];

if (l[3] != null) {
  alert("YESSS!");
}

In Coffeescript, how would I express l[3] !== "undefined" ?

Dan K.K. · Accepted Answer · 2012-11-09 10:15:53Z

1

Just add typeof operator, like this:

if typeof l[3] != 'undefined'
  alert 'Yes!'

answered Nov 9, 2012 at 10:15

Dan K.K.

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Comments

epidemian · Accepted Answer · 2012-11-09 12:27:43Z

1

Beware that l[3] !== "undefined" is asking whether l[3] is different from the string that says "undefined", not if its value isn't undefined. The comparison that CoffeeScript generates for l[3]? -> l[3] != null will verify when l[3] is some value different from undefined or null, which is what you want to ask most of the time :)

answered Nov 9, 2012 at 12:27

epidemian

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