Polymer, paper-datatable styling of rows - polymer

Question

I'm trying to colour the rows of paper-datatable
using the attribute customRowStyle
This Plunk of paper-datatable is working, rows are colored, but it's not enclosed as separate Polymer element.
I need to enclose paper-datatable in separate element.
Need some help to fix this:
how to make customRowStyle(item) to get called on table render and pass the item?
<paper-datatable data="{{data}}"
custom-row-style="{{generateRowCss}}"
on-row-tap="row_tap">
<paper-datatable-column header="title" property="title"></paper-datatable-column>
<paper-datatable-column header="Calories" property="calories"></paper-datatable-column>
<paper-datatable-column header="Fat (g)" property="fat" ></paper-datatable-column>
</paper-datatable>
...
generateRowCss: function (item) {
console.log('theming_2 generateRowCss:');
var levels = ['#FFFFFF', '#FFEBEE', '#FFCDD2', '#EF9A9A'];
var min = 150;
var max = 450;
var level = Math.floor((item.calories - min) / (max - min) * levels.length);
return 'background:' + levels[level] + ';';
},
EDIT:
Plunk with #a1626 solution.

Answer 1

As generateRowCssthat is passed to customRowStyle is a function rather than the return value of the function(which is what your code is passing) you'll have to do something like this. Instead of creating a function generateRowCss create a property with the same name, initialize it as Object and return its value as whole function
properties: {
data: {
type: Array,
notify: true,
value: [
{id: 0, title: 'Frozen yogurt', calories: 159, fat: 6},
{id: 1, title: 'Ice cream sandwich', calories: 237, fat: 9},
{id: 2, title: 'Eclair', calories: 262, fat: 16},
{id: 3, title: 'Cupcake', calories: 305, fat: 3.7},
],
},
generateRowCss:{
type:Object, //this is optional you can skip this also
value:function(){
return function(item){
console.log('app.generateRowCss');
console.log(item);
var levels = ['#FFFFFF', '#FFEBEE', '#FFCDD2', '#EF9A9A'];
var min = 150;
var max = 450;
var level = Math.floor((item.calories - min)/(max-min)*levels.length);
console.log(level);
console.log('background:'+levels[level]+';');
return 'background:'+levels[level]+';';
}
}
}
},
Pasted above are the properties of your custom element. Here is the working plunkr