How can I convert the "arguments" object to an array in JavaScript?
ES6 using rest parameters
If you are able to use ES6 you can use:
function sortArgs(...args) { return args.sort(function (a, b) { return a - b; });}document.body.innerHTML = sortArgs(12, 4, 6, 8).toString();As you can read in the link
The rest parameter syntax allows us to represent an indefinite number of arguments as an array.
If you are curious about the ... syntax, it is called Spread Operator and you can read more here.
ES6 using Array.from()
Using Array.from:
function sortArgs() { return Array.from(arguments).sort(function (a, b) { return a - b; });}document.body.innerHTML = sortArgs(12, 4, 6, 8).toString();Array.from simply convert Array-like or Iterable objects into Array instances.
ES5
You can actually just use Array's slice function on an arguments object, and it will convert it into a standard JavaScript array. You'll just have to reference it manually through Array's prototype:
function sortArgs() { var args = Array.prototype.slice.call(arguments); return args.sort();}Why does this work? Well, here's an excerpt from the ECMAScript 5 documentation itself:
NOTE: The
slicefunction is intentionally generic; it does not require that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method. Whether theslicefunction can be applied successfully to a host object is implementation-dependent.
Therefore, slice works on anything that has a length property, which arguments conveniently does.
If Array.prototype.slice is too much of a mouthful for you, you can abbreviate it slightly by using array literals:
var args = [].slice.call(arguments);However, I tend to feel that the former version is more explicit, so I'd prefer it instead. Abusing the array literal notation feels hacky and looks strange.
It's also worth referencing this Bluebird promises library wiki page that shows how to manage the arguments object into array in a way that makes the function optimizable under V8 JavaScript engine:
function doesntLeakArguments() { var args = new Array(arguments.length); for(var i = 0; i < args.length; ++i) { args[i] = arguments[i]; } return args;}This method is used in favor of var args = [].slice.call(arguments);. The author also shows how a build step can help reduce the verbosity.
function sortArgs(){ return [].slice.call(arguments).sort() }// Returns the arguments object itselffunction sortArgs(){ return [].sort.call(arguments) }Some array methods are intentionally made not to require the target object to be an actual array. They only require the target to have a property named length and indices (which must be zero or larger integers).
[].sort.call({0:1, 1:0, length:2}) // => ({0:0, 1:1, length:2})