How to convert a DOM node list to an array in Javascript?

NodeLists are host objects, using the Array.prototype.slice method on host objects is not guaranteed to work, the ECMAScript Specification states:

Whether the slice function can be applied successfully to a host object is implementation-dependent.

I would recommend you to make a simple function to iterate over the NodeList and add each existing element to an array:

function toArray(obj) {
  var array = [];
  // iterate backwards ensuring that length is an UInt32
  for (var i = obj.length >>> 0; i--;) { 
    array[i] = obj[i];
  }
  return array;
}

UPDATE:

As other answers suggest, you can now can use in modern environments the spread syntax or the Array.from method:

const array = [ ...nodeList ] // or Array.from(nodeList)

But thinking about it, I guess the most common use case to convert a NodeList to an Array is to iterate over it, and now the NodeList.prototype object has the forEach method natively, so if you are on a modern environment you can use it directly, or have a pollyfill.

In es6 you can just use as follows:

• Spread operator

   var elements = [... nodelist]
  

• Using Array.from

   var elements = Array.from(nodelist)
  

more reference at https://developer.mozilla.org/en-US/docs/Web/API/NodeList