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array ref.length = 7 (0 - 6), and I want to try to match ref[0]['x'] to ref[1]['x'] I am doing this:

   for(var i=0;i<ref.length;i++){
      if( ref[i]['x'] != ref[i+1]['x'] && ref[i+1]['x'].length > 0 )
         //do something
   }

The for loop is iterating all the way to array number 6 then element 6+1 is blank so I get an error on the if statement line saying ref[i+1] is undefined....

is there a better way to do this?

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5 Answers

up vote 1 down vote accepted 
for (var i=0; i<ref.length-1; i++) { // Note the "-1".

This way when you use the index i+1 you're still in bounds.

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up vote 3 down vote

Better:

for (var i=ref.length-2;i>=0;i--)

Javascript will evaluate the condition on each iteration, so it's generally preferable go backwards instead. With this construct "ref.length" is only evaluated once. Another alternative I like which will perform the same:

var i=ref.length-1;
while (i--) {

}

(Normally you'd be i=ref.length-1 in the first example, and i=ref.length in the second, but you're trying to stay one less than the array length).

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up vote 1 down vote

for (var i = 0; i < ref.length - 1; i++)

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Am I the only one who likes foreplay and maybe a bit of conversation before and after the act? – Jean-François Corbett May 28 '11 at 14:04
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up vote 0 down vote

What about:

for(var i=0;i<ref.length-1;i++){
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up vote 0 down vote

If you just use ref.length-1 won't that solve your problem? I might not fully understand what you're asking.

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