Comparing NodeList iteration methods: Using Array.prototype.forEach.call() versus Array.from().forEach

Question

Comparing NodeList iteration methods: Using Array.prototype.forEach.call() versus Array.from().forEach

I've been looking for a simple method to iterate through nodelists, and I've always found it frustrating that I can't just use forEach directly on nodeLists.

Instead, I've come up with this approach:

Array.prototype.forEach.call(nodeList, callback)

.

For obtaining the index, I utilize:

Array.prototype.indexOf.call(nodeList, node)

.

In fact, I tend to rely on Array.prototype for many operations involving nodeLists.

But I can't help but wonder if these methods are considered unconventional workarounds?

Is there a more proper way to achieve the same results?

Moreover, assuming that I don't actually require an array from nodeList, would using

Array.from(nodeList).forEach(callback)

offer any benefits?

javascript arrays foreach prototype nodelist

Answer 1

Answer №1

Using

Array.prototype.forEach.call(nodeList, callback)

applies the logic of the forEach method to the node list. The forEach function essentially contains a `for` loop that iterates from index `0` to `this.length`, calling a callback on each item. By passing the node list as the `this` value in the `forEach` call, everything runs smoothly due to the similarities between node lists and arrays.

On the other hand,

Array.from(nodeList).forEach(callback)

creates a new array from the node list and then uses the `forEach` method on this new array. This can be simplified into two clearer lines:

var newArray = Array.from(nodeList);  // create a new array from the node list
newArray.forEach(callback);           // apply forEach on the new array

The first method is preferable as it avoids creating unnecessary additional resources and works directly on node lists.

Answer 2

Using

Array.prototype.forEach.call(nodeList, callback)

applies the logic of the forEach method to the node list. The forEach function essentially contains a `for` loop that iterates from index `0` to `this.length`, calling a callback on each item. By passing the node list as the `this` value in the `forEach` call, everything runs smoothly due to the similarities between node lists and arrays.

On the other hand,

Array.from(nodeList).forEach(callback)

creates a new array from the node list and then uses the `forEach` method on this new array. This can be simplified into two clearer lines:

var newArray = Array.from(nodeList);  // create a new array from the node list
newArray.forEach(callback);           // apply forEach on the new array

The first method is preferable as it avoids creating unnecessary additional resources and works directly on node lists.

Answer 3

Answer №2

One approach that is compatible with ES5 is as follows:

Array.prototype.forEach.call(nodeList, callback).

Another method utilizes Array.from, a feature introduced in ES6:

Array.from(nodeList).forEach(callback)

It's worth noting that the use of Array.from can be optimized by leveraging its second argument:

Array.from(nodeList, callback)

This optimization allows for the entire operation to occur in just one iteration.

An interesting aspect is that the callback serves as a mapping function in the above expression. For example, you can create an array containing the text content of nodes like this:

texts = Array.from(nodeList, node => node.textContent)

Caveat

If you use Array.from with a callback on a live node list (see NodeList) and modify the node list within the callback, unexpected effects may occur. In such cases, it is recommended to first convert the node list into an array before applying the callback to its entries.

Answer 4

One approach that is compatible with ES5 is as follows:

Array.prototype.forEach.call(nodeList, callback).

Another method utilizes Array.from, a feature introduced in ES6:

Array.from(nodeList).forEach(callback)

It's worth noting that the use of Array.from can be optimized by leveraging its second argument:

Array.from(nodeList, callback)

This optimization allows for the entire operation to occur in just one iteration.

An interesting aspect is that the callback serves as a mapping function in the above expression. For example, you can create an array containing the text content of nodes like this:

texts = Array.from(nodeList, node => node.textContent)

Caveat

If you use Array.from with a callback on a live node list (see NodeList) and modify the node list within the callback, unexpected effects may occur. In such cases, it is recommended to first convert the node list into an array before applying the callback to its entries.

Answer 5

Answer №3

const convertedArray = Array.from(nodeList);
//later on
const secondConvertedArray = Array.from(nodeList);

Upon comparing these arrays, you will notice that they may not be exactly the same. NodeLists are dynamic and reflect changes in the DOM, while the arrays created using Array.from remain static. If this behavior is what you need or if you are indifferent to this distinction, then it's all good. However, it's important to note that Array.from is a relatively new feature and may not be supported by older browsers, so caution should be exercised when using it in production environments (unless you are using something like Babel).

Answer 6

const convertedArray = Array.from(nodeList);
//later on
const secondConvertedArray = Array.from(nodeList);

Upon comparing these arrays, you will notice that they may not be exactly the same. NodeLists are dynamic and reflect changes in the DOM, while the arrays created using Array.from remain static. If this behavior is what you need or if you are indifferent to this distinction, then it's all good. However, it's important to note that Array.from is a relatively new feature and may not be supported by older browsers, so caution should be exercised when using it in production environments (unless you are using something like Babel).

Comparing NodeList iteration methods: Using Array.prototype.forEach.call() versus Array.from().forEach

Answer №1

Answer №2

Caveat

Answer №3

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