Question: I've tried to build <https://github.com/DEVSENSE/Phalanger>, but after the build process it shows build errors. I tried VS 2015, maybe there it just a question of a wrong version?

[![screenshot](https://i.stack.imgur.com/Q6qXv.png)](https://i.stack.imgur.com/Q6qXv.png)

Answer: 
As per [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in),

> 
> The in operator returns true if the specified property is in the specified object.
> 
> 
> 

`in` will check for keys. Its similar to `Object.keys(array).indexOf(test)`

```js
var a1 = [1,2,3];
var a2 = ['a', 'b', 'c']
var test = 2;

console.log(test in a1)
console.log(test in a2)

// Ideal way

//ES5
console.log(a1.indexOf(test)>-1)
console.log(a2.indexOf(test)>-1)

//ES6
console.log(a1.includes(test))
console.log(a2.includes(test))
```
Try this

```
var test = 2;
var arrval= [1, 5, 2, 4];
var a = arrval.indexOf(test);
if(a>-1) console.log("Having");
else console.log("Not Having");

```