Why doesn't .join() work with function arguments?

Question

Why does this work (returns \"one, two, three\"):

var words = [\'one\', \'two\', \'three\'];
$(\"#main\").append(\'
\' + words.join(\", \") + \'         


        

Answer 1

At the moment you can't join array arguments, because they aren't an array, shown here

so you have to either first turn them into an array like this,

function f() {
  var args = Array.prototype.slice.call(arguments, f.length);
  return 'the list: ' + args.join(',');
}

or like this, a bit shorter

function displayIt() {
  return 'the list: ' + [].join.call(arguments, ',');
}

if you are using something like babel or a compatible browser to use es6 features, you can also do this using rest arguments.

function displayIt(...args) {
  return 'the list: ' + args.join(',');
}

displayIt('111', '222', '333');

which would let you do even cooler stuff like

function displayIt(start, glue, ...args) {
  return start + args.join(glue);
}

displayIt('the start: ', '111', '222', '333', ',');