Concatenating strings with `if` statements in JavaScript

Question

I\'m attempting to set up a script to concatenate some variables inside a string if they exist, in order to place the appropriate metadata tags into a rendered HTML

Answer 1

I'd use a ternary operator:

data = "\n"
     + "\n" 
     + ( typeof metadata_title  !== "undefined" ?  "\n"                             : "" )
     + ( typeof metadata_author !== "undefined" ?  "\n" : "" )
     + ( typeof metadata_date   !== "undefined" ?  "\n"     : "" )
     + "\n"
     + "\n"
     + "\n"
     + paras.join("\n\n")
     + "\n"
     + "\n"
     + "\n"
     + ""
;