Question: How can we concatenate an expression value with some string and evaluate the resulting expression?

If we have one object prefix and I wanted to concatenate its value with some string. e.g 

```
{{prefix"Output"}}

```

I would like to first evaluate the prefix value and then concatenate it with the "Output" string. 

So the resulting expression may be something like "UnitOutput" where Unit is the value of the prefix.

Lastly I want the concatenated expression from above to be evaluated as well in that case resulting value will be the value of "UnitOutput".

Answer: 
You can do this with SASS. If you haven't already type into terminal

```
$ ionic setup sass

```

You can then use the overrides inside the scss/ directory.

```
$light:                           #fff !default;
$stable:                          #f8f8f8 !default;
$positive:                        #387ef5 !default;
$calm:                            #11c1f3 !default;
$balanced:                        #33cd5f !default;
$energized:                       #ffc900 !default;
$assertive:                       #ef473a !default;
$royal:                           #886aea !default;
$dark:                            #444 !default;

```

I highly recommend using a CSS pre-processor for Ionic, they have a great lib with everything in variables for you.
Override this Ionic Sass Variable in themes/variables.scss

```css
$toolbar-background:#FFFFFF;
```

[You can find other Ionic Sass Variable list here:](http://ionicframework.com/docs/v2/theming/overriding-ionic-variables/)