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Loop Over querySelectorAll Matches

You can loop over Arrays really easily in JavaScript with forEach, but unfortunately it's not that simple with the results of a querySelectorAll.

/* Will Not Work */
document.querySelectorAll('.module').forEach(function() {
  
});

That's because what you get back from querySelectorAll isn't an array, it's a (non-live) NodeList.

Here's a quick way to iterate over all the found elements:

var divs = document.querySelectorAll('div');

[].forEach.call(divs, function(div) {
  // do whatever
  div.style.color = "red";
});

Fair warning, Todd Motto explains why this method is a rather hacky, detailing over 10 problems with it.


You could also use a classic for loop:

var divs = document.querySelectorAll('div'), i;

for (i = 0; i < divs.length; ++i) {
  divs[i].style.color = "green";
}

Todd's suggestion is to make your own method:

// forEach method, could be shipped as part of an Object Literal/Module
var forEach = function (array, callback, scope) {
  for (var i = 0; i < array.length; i++) {
    callback.call(scope, i, array[i]); // passes back stuff we need
  }
};

// Usage:
// optionally change the scope as final parameter too, like ECMA5
var myNodeList = document.querySelectorAll('li');
forEach(myNodeList, function (index, value) {
  console.log(index, value); // passes index + value back!
});

There are also for..of loops, but...

/* Be warned, this only works in Firefox */

var divs = document.querySelectorAll('div );

for (var div of divs) {
  div.style.color = "blue";
}

This is pretty intense (probably dangerous and generally not recommended) but you could make NodeList have the same forEach function as Array does, then use it.

NodeList.prototype.forEach = Array.prototype.forEach;

var divs = document.querySelectorAll('div').forEach(function(el) {
  el.style.color = "orange";
})

There is a bit more information in the MDN article.

Comments

  1. Aneece
    Permalink to comment#

    The safer way to do the last version and co-opt the Array method would be to do something like this:

    Array.prototype.forEach.call(document.querySelectorAll('div'), function(div) { console.log(div); })
    

    Of course, you still need to make sure you have a polyfill for Array.forEach if you’re targeting older browsers.

  2. b
    Permalink to comment#

    Hey this saved me some time – I was curious why I couldn’t loop over with forEach. Thanks!

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