Is it bad practice to use the same variable name in multiple for-loops?

Question

I was just linting some JavaScript code using JSHint. In the code I have two for-loops both used like this:

for (var i = 0; i < somevalue; i++) { ... }
         


        

Answer 1

I know this question has been answered, but if you want super for loops, write them like this:

var names = ['alex','john','paul','nemo'],
    name = '',
    idx = 0,
    len = names.length;

for(;idx

A couple of things going on here...

1. The array length is being stored in len. This stops JS evaluating names.length every iteration

2. The idx increment is a PRE-INCREMENT (e.g. ++idx NOT idx++). Pre-increments are natively faster than Post-increments.

3. The storing of a reference to name. This is optional but recommended if you'll be using the name variable a lot. Every call to names[idx] requires finding the index in the array. Whether this search be a linear search, tree search or hash table, the find is still happening. So store a reference in another variable to reduce lookups.

Finally, this is just my personal preference, and I have no proof or any performance benefits. However I always like initialising variables to the type they're going to be e.g. name = '',.