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Comment by __ryan__ | Hacker News Reader

I’m not super familiar with Clojure, but I tried to read through the link you shared. I certainly could be missing something, what can Clojure’s destructuring do that JavaScript cannot?

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I'm not sure what are all the differences but one I have come across that you can't do in JS is to simultaneously destructure an object/array, and at the same time bind a name to the entire object/array. For instance here in Clojure we can extract the a,b,c keys from the passed map, and at the same time bind the whole map to the variable bar.

    (defn foo [{:keys [a b c] :as bar}]
      [bar a b c])

    (foo {:a 1 :b 2 :c 3}) ;; => [{:a 1, :b 2, :c 3} 1 2 3]

in JS you can do

    const f = ({a,b,c}) => [???, a, b, c]

but how do you bind to the whole object as well?

Oh I thought of an other one. In Clojure "objects" are actually maps, which can have non-string keys as well. That means you can destructure maps which have non-string (or, technically, keyword) keys as well:

    (defn foo [{a 1 
                b 2 :as bar}]
      [bar a b])

    (foo {1 "hi" 2 "world" 3 "!"}) ;; => [{1 "hi", 2 "world", 3 "!"} "hi" "world"]

In JS of course you can have Maps with non-string keys, but destructuring doesn't work on them. Plus you have other issues like arrays in JS having equality defined by reference rather than value, making maps less useful overall.

Ah, I see. Yeah, you would have to bind the argument to a name then destructure it separately:

  let foo = (bar) => {
    let {a, b, c} = bar
    return [bar, a, b, c]
  }

    foo({ a: 1, b: 2, c: 3 }) // => [ { a: 1, b: 2, c: 3 }, 1, 2, 3 ]

Though JavaScript object keys are strictly strings and symbols, you can destructure dynamic keys like so:

  let foo = (bar) => {
    let {[1]: a, [2]: b} = bar
    return [bar, a, b]
  }

  foo({ 1: "hi", 2: "world", 3: "!" }) // => [ { '1': 'hi', , '2': 'world', '3': '!' }, 'hi' 'world' ]

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