Get keys from both arrays and objects using one function in JavaScript

Question

I need a function to get the keys from objects, and the entries from arrays, like so:

_key(["x", "y", "z"]); // ["x", "y", "z"];
_key({ a: "x", b: "y", c: "z" }); // ["a", "b", "c"];

Is there a built-in way to do this, and if not, what's the shortest possible method?

Answer 1

You can first test it if it's array with Array.isArray()

 function _key(data) { return Array.isArray(data) ? data : Object.keys(data); } console.log(_key(["x", "y", "z"])) console.log(_key({ a: "x", b: "y", c: "z" })) 

If you need for example to pass multiple parameters, object and arrays you can use rest parameter syntax and map() to return one array.

 function _key(...data) { return [].concat(...data.map(e => Array.isArray(e) ? e : Object.keys(e))) } console.log(_key(["x", "y", "z"], { a: "x", b: "y", c: "z" }, {z: 1})) 

Answer 2

function values(object) {
  return (object instanceof Array) ? object : Object.keys(object);
}

Answer 3

You could test if it is an array or not and return either the values or the keys of the object. I works with ES6 only.

 function _key(data) { return Object[['keys', 'values'][+Array.isArray(data)]](data); } console.log(_key(["x", "y", "z"])) console.log(_key({ a: "x", b: "y", c: "z" })) 

Answer 4

Thanks for all the answers, guys! Here's what I did:

_key = function (_) {   
    let u = [].slice.call(_), v = Object.values(_).length;
    return u.length >= v ? toString.call(_) == "Array" ? _ : u : keys(_);
};

This works on arrays, pseudo-arrays (like arguments), objects, and pseudo-objects (like window)

It works by using some weird behavior, which can be tested with this snippet:

 _test = function (x, y) { console.log(y + ":", [].slice.call(x).length + "-" + Object.values(x).length); }; console.log("Input: AB"); _test(["x"], "Array"); _test({ x: "" }, "Object"); _test(document.querySelectorAll("div"), "Pseudo-Array"); _test(document, "Pseudo-Object"); 

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