JavaScript Increment Operator isn't working?

Question

So for some reason, when I use the increment operator in this code, it doesn't work. I've verified my variables are numbers.. Not sure what's going on.

var fs = require('fs')
 , bt = require('buffertools')
var start = 0;
fs.readFile(process.argv[2], function(err, data) {
 console.log(data);
 while (bt.indexOf(data, '\n', start)) {
 var nl = bt.indexOf(data, '\n', start); // nl is 40
 console.log(start, nl); // 0, 40
 console.log(data.slice(start, nl)); // works great!
 start = nl++; // reset the offset past that last character..
 console.log(start, typeof start); // start == 40? the heck? 'number'
 process.exit(); // testing
 //console.log(nl, start); 40, 40
 }
});

EDIT ------

And the solution...

"use strict";
var fs = require('fs')
 , bt = require('buffertools');
fs.readFile(process.argv[2], function(err, data) {
 var offset = 0;
 while (true) {
 var nl = bt.indexOf(data, '\n', offset);
 if (nl === -1) break;
 console.log(data.slice(offset, nl));
 offset = ++nl;
 }
 console.log(data.slice(offset));
});

Thanks!

• gen_Eric: nl++. What this does is increment nl and return the original value. Try start = ++nl. ++nl will increment nl and return the new value.

Answer 1

You're looking for ++nl and not nl++ , num++ increments the number and returns the old value.

• num++ is the postfix increment operator - as you can see, its description says "Return oldValue."

• ++num is the prefix incremenet operator - as you can see, its description says "Return newValue."

This is true in many other languages too by the way.

---

Since you're not changing nl later at all, you can write this as:

 start = nl + 1;

Which is clearer.

• sent1nel: Interesting. I've never run into that before, thanks. Will accept in 12 minutes.