"Unraveling the Mysteries of the Basic JavaScript

Question

"Unraveling the Mysteries of the Basic JavaScript

This scenario involves the task of eliminating all paragraphs. Despite using a for-loop, not all paragraphs were successfully removed. The initial paragraph remained unaltered. http://codepen.io/vinhnghi223/pen/jnkzh

article=document.getElementsByTagName("article")[0];

for (i=0; i<article.childNodes.length; i++) {
 article.removeChild(article.lastChild);
}

On the contrary, modifying the code to use i<4 (which is less than article.childNodes.length, resulting in 5) solves the issue.

The perplexity arises from the fact that article.childNodes.length returns 5. Although it seems logical that if it works with 4 items, it should work with 5 as well.

javascript for-loop

Answer 1

Answer №1

One reason for this behavior is that the .childNodes collection updates each time a removal occurs. As a result, the .length decreases with each iteration while the index i increases. Removing the .lastChild causes the loop to meet in the middle, leaving the first half untouched.

To avoid this issue, hard code the original length of the children list.

If you want to remove all the children nodes, simply check if a .lastChild exists within the loop condition.


while (article.lastChild) {
    article.removeChild(article.lastChild);
}

Dealing with "live" node lists like this can be challenging, so it's important to exercise caution when modifying elements within a loop.

Answer 2

One reason for this behavior is that the .childNodes collection updates each time a removal occurs. As a result, the .length decreases with each iteration while the index i increases. Removing the .lastChild causes the loop to meet in the middle, leaving the first half untouched.

To avoid this issue, hard code the original length of the children list.

If you want to remove all the children nodes, simply check if a .lastChild exists within the loop condition.


while (article.lastChild) {
    article.removeChild(article.lastChild);
}

Dealing with "live" node lists like this can be challenging, so it's important to exercise caution when modifying elements within a loop.

Answer 3

Answer №2

The reason for this behavior is due to the fact that you are modifying the collection of elements while looping through it. As you iterate from zero upwards, you are also removing child nodes at the same time, causing the loop's upper limit to decrease. Consequently, your loop counter will eventually reach the diminishing number of child nodes, resulting in the loop terminating prematurely.

To ensure the loop functions correctly, it is essential to retain the original count of child nodes:

var cnt = article.childNodes.length;
for (i = 0; i < cnt; i++) {
  article.removeChild(article.lastChild);
}

Alternatively, you can continuously remove child nodes as long as there are any remaining:

while (article.childNodes.length> 0) {
  article.removeChild(article.lastChild);
}

Answer 4

The reason for this behavior is due to the fact that you are modifying the collection of elements while looping through it. As you iterate from zero upwards, you are also removing child nodes at the same time, causing the loop's upper limit to decrease. Consequently, your loop counter will eventually reach the diminishing number of child nodes, resulting in the loop terminating prematurely.

To ensure the loop functions correctly, it is essential to retain the original count of child nodes:

var cnt = article.childNodes.length;
for (i = 0; i < cnt; i++) {
  article.removeChild(article.lastChild);
}

Alternatively, you can continuously remove child nodes as long as there are any remaining:

while (article.childNodes.length> 0) {
  article.removeChild(article.lastChild);
}

"Unraveling the Mysteries of the Basic JavaScript

Answer №1

Answer №2

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