pass Polymer data binding through a Javascript function

You could use expression filter for that:

<template repeat="{{ p in grid_points }}">    <core-item>{{ p | grid_to_geodetic }}</core-item></template>...<script>  Polymer('your-element', {    grid_to_geodetic: function(point){       return point.x + point.y;    }  });</script>

Filter takes one value and returns one, if you need to convert x and y separately you have to use an constant parameter to indicate which part of the point you want to convert, something like

<template repeat="{{ p in grid_points }}">    <core-item>{{ p | grid_to_geodetic(1) }}</core-item>    <core-item>{{ p | grid_to_geodetic(2) }}</core-item></template>...<script>  Polymer('your-element', {    grid_to_geodetic: function(point, part){       if(part == 1) return point.x;       else return point.y;    }  });</script>

I did manage to invoke it thanks to some ideas from ain:

So with the expression filter you are telling the template to invoke a Dart function:

<template repeat="{{ p in start_points }}">    <core-item>{{ p | rt90_to_wgs84 }}</core-item></template>

Then in the Dart backing class you add a function with the same name as in the filter and you call a global js function with context.callMethod('funcion_name', [args_list]);:

rt90_to_wgs84(p) {  return context.callMethod('grid_to_geodetic', [p.x, p.y]);}