using javascript calculated values in less

In LESS I used following code to get the window's height.

@winheight:`$(window).height()`

What I'm getting is a number, but when i add px there to have the unit,

height: @winheight px;

It will compile to something like height: 910 px.

I tried to have the unit after the javascript evaluation too. but I got the same result.

@winheight:`$(window).height()`px
height: @winheight;
...

height:910 px;

How can I get height:910px there (without the space between number and unit) ?

EDIT:

As for the first four results, it creates a string height:"910px", which doesn't render correctly.