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

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";