 El-Cortez - 4 years ago 134
Javascript Question

# Javascript Permutations magic trick

I'm reading some algorithms to try and understand permutations in javascript, and the following one quite stunned me

``````var permArr = [], usedChars = [];
function permute(input) {
var i, ch, chars = input.split('');
for (i = 0; i < chars.length; i++) {
ch = chars.splice(i, 1);
usedChars.push(ch);
if (chars.length == 0) permArr[permArr.length] = usedChars.join('');
permute(chars.join(""));
chars.splice(i, 0, ch);
usedChars.pop();
}
return permArr
}
``````

FYI I found this algorithm on the following website: http://staff.roguecc.edu/JMiller/JavaScript/permute.html

I can see that this algorithm works, but there is a line that confuses me and I can't find anywhere where it works

``````var i, ch, chars = input.split("");
``````

If i console.log(i) or console.log(ch) before OR after in the code, it returns undefined everywhere.
If i remove i and ch, the algorithm does not work anymore.

Can someone explain me this line and how it works?
Thanks a lot nozzleman
Answer Source

### No Magic involved

``````var i, ch, chars = input.split('');
``````

declares the variables `i`, `ch` and `chars` and assigns to `chars` what `input.split('')` returns.

Basically its equivalent to

``````var i; // undefined
var ch; // undefined
var chars = input.split(''); // Array of string
``````

This is typically done for the variables to be available across loop iterations (to access previous values).

### However...

`i` is just the loop varible and could be declared inline as in

``````for (var i = 0; i < chars.length; i++) {
``````

`ch` could live inside the loop since it is reassigned in the first statement anyway

``````  for (var i = 0; i < chars.length; i++) {
var ch = chars.splice(i, 1);
``````

which makes the example confusing indeed (one could say it's poorly written)

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