I'm currently reading a book called "JavaScript and jQuery Interactive Front End Web Developement" by Jon Duckett. In the chapter on DOM, it mentions that
NodeLists look like arrays and are numbered like arrays, but they are not actually arrays. they are a type of object called a collection.
My question is, what is the difference between an array and collection in JavaScript and when should I choose one over the other?
From https://developer.mozilla.org/it/docs/Web/API/NodeList:
Why is NodeList not an Array?
NodeList are used very much like arrays and it's tempting to invoke Array.prototype methods on them, however NodeList objects don't have any of the familiar Array methods.
JavaScript has an inheritance mechanism based on prototypes for both built–in objects (like Arrays) and host objects (like NodeLists). Array instances inherit array methods (such as forEach or map) because their prototype chain looks like the following:
myArray --> Array.prototype --> Object.prototype --> null (The prototype chain of an object can be obtained by calling Object.getPrototypeOf several times.)
forEach, map and the likes are own properties of the Array.prototype object.
Unlike arrays, NodeList prototype chain looks like the following:
myNodeList --> NodeList.prototype --> Object.prototype --> null
NodeList.prototype contains the item method, but none of the Array.prototype methods, so they cannot be used on NodeLists.
NodeLists are very similar to Array collections of elements, often referred to as “array-like”, but with a subtle difference - you’re missing out on a lot of JavaScript functionality by keeping your collection as a NodeList, such as true Array iteration and Prototypal methods.
The NodeList interface provides the abstraction of an ordered collection of nodes, without defining or constraining how this collection is implemented.
NodeList to array
var myArray = Array.prototype.slice.call(myList, 0); undefined myArray.constructor.toString(); "function Array() { [native code] }"
