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I save the reference of document method:

let qs = document.querySelector;

Then try to get the element:

btnSort = qs('button');

Why does this method not work as for references to simple functions?

Dharman
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Zero.One.Zero
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    Because you lose the context. `querySelector` can be invoked from different elements, not just `document`, so it relies on `this`. When you reassign the reference and invoke the new variable, you lose the `this` context. – VLAZ Sep 18 '19 at 06:10

1 Answers1

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Because this in JavaScript is determined in runtime.

document.querySelector(...) // this -> document


let qs = document.querySelector

qs(...) // In this case `this` refer to the global object, which is window in a browser

You need to bind this when you created a function reference.

let qs = document.querySelector.bind(document)

Or giving a this binding when you call it.

qs.call(document, 'button')
Jian
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