jQuery: String & number concatenation returning NaN

jQuery string & number concatenation.js

//Scenario 1: String & Math calculation
"height :" + $(document).height() - $(window).height(); 
//Result: NaN

//Scenario 2: String & Math calculation with parentheses
"height :" + ($(document).height() - $(window).height()); 
//Result: Height : 1870

//Scenario 3: String without match calculation
"Height:" + $(document).height();
//Result: Height737

//Scenario 4: Match Calculation & String
$(document).height() - $(window).height() + "Height";
//Result: 1870Height

//Scenario 5: String & Match calculation (Converting math output to string)
"Height" + String($(document).height() - $(window).height());
//Result: Height:1870