Spread operator breaks on HTML Collection or NodeList with [email protected]

[utsavchatterjee]

Let htmlCollection be an HTMLCollection {} such that,

Object.keys(htmlCollection) is [‘0’, ‘1’, ‘2’]

Object.values(htmlCollection) is [ HTMLDivElement {}, HTMLDivElement {}, HTMLDivElement {} ]

Using tslib <= 2.2.0

[ …htmlCollection ] gives [ HTMLDivElement {}, HTMLDivElement {}, HTMLDivElement {} ]

Using tslib 2.3.0

[ …htmlCollection ] gives [ HTMLCollection {} ], where HTMLCollection {} is the same as htmlCollection

Similar behaviour is observed for NodeList {}.

[rbuckton]

Apparently NodeList and HTMLCollection do not have [Symbol.isConcatSpreadable]: true, so the array concat adds them as an element instead of adding their elements.