Handling of corner cases for 'fn.concat'

[amoilanen]

fn.concat(6, [1, 2, 3]) or fn.concat() worked differently from how I would expect them to work. In both cases an exception would be thrown. At the same time it is perfectly fine to call standard methods like arr1.concat(6) and arr1.concat(), in the first case it will just append 6 and in the second case will leave the array unchanged.

I added a few test cases covering those corner cases and modified the implementation of fn.concat a bit to handle them.

Basically I just looked at the following examples for Array.prototype.concat and String.prototype.concat and made sure that the behavior is similar for fn.concat:

var arr1 = [1, 2, 3];
var arr2 = [4, 5, 6];

console.log(arr1.concat()); //[1, 2, 3]
console.log(arr1.concat(null)); //[1, 2, 3, null]
console.log(arr1.concat((void 0))); //[1, 2, 3, undefined]
console.log(arr1.concat("4")); //[1, 2, 3, "4"]
console.log(arr1.concat(arr2)); //[1, 2, 3, 4, 5, 6]

var str1 = "123";
var str2 = "456";

console.log(str1.concat(str2)); //"123456"
console.log("".concat(str2)); //"456"
console.log(str1.concat("")); //"123" 

By the way, I assumed that fn.concat should also work with strings, not only arrays.

Please, let me know if you have any notes or suggestions.

[eliperelman]

This PR has bitrotted with the 0.8.0 released. Please rebase and refactor, and resubmit for review (wow that was a lot of "re"s :smile:)

[amoilanen]

I merged the recent changes :) Can you, please, take a look?

[eliperelman]

To me this was a bug in my implementation. I have merged your changes and tagged this for release v0.8.1. Thanks for your contribution!

[amoilanen]

OK. Thank you!