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

Build up the entire document into an array, then join with a "\n" at the end. (The rationale for this is of course to not have lots of new lines scattered all about! And if you are on IE7 or less, Array#join is considerably faster than repeated string concatenation.)

Code here: http://jsfiddle.net/ZCbCZ/

UPDATE I forgot to include the "paras" in the first fiddle. The code with the paras is here: http://jsfiddle.net/U8325/1/

For those not wishing to click through and try it out, here is the script:

// Not going to define metadata_author just to be saved by typeof :-)
var metadata_title = "Hello";
var metadata_date = "2011-09-07";

// Okay 3 paras for fun
var paras = ["
paragraph1
", "
paragraph2
", "
paragraph3
"];

data = ["", ""]

if (typeof metadata_title !== "undefined") {
    data.push("");
}
if (typeof metadata_author !== "undefined") {
    data.push("");
}
if (typeof metadata_date !== "undefined") {
    data.push("");
}

data.push("");
data.push("");
paras.forEach(function (p) {data.push(p);});   // Requires ES5; use a for-loop if you don't have it
data.push("");
data.push("");
data = data.join("\n");
alert(data);