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JavaScript

Posted by Gaurav Yadav
Gaurav Yadav
5,047 Points

Behaviour of javascript interpreter

my html file :

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<ul>
    <li>Grapes</li>
</ul>
<script src="script.js"></script>
</body>
</html>

My js file: 

const ul = document.querySelector("ul");
const firstListItem = ul.firstElementChild;
console.log(firstListItem);
const button = document.createElement("button");
button.textContent = "I have been added later";
firstListItem.appendChild(button);

So, what I have learnt is that javascript interpreter goes line by line and executes code. So when i log out firstListItem, it should log out just 

<li>Grapes</li>

Why does it log out 

<li>Grapes<button>I have been added later</li>

because, I added button later in my js code, shouldn't it just log out Grapes?

1 Answer

james south
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points
james south
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points

it is, it is just happening so fast that by the time the console updates the button has been added. i added a timeout of 100 ms before the button is added and it logs what you expected. if 100 isn't enough on your computer increase it.

const ul = document.querySelector("ul");
const firstListItem = ul.firstElementChild;
console.log(firstListItem);
const button = document.createElement("button");
button.textContent = "I have been added later";
window.setTimeout(() => 
firstListItem.appendChild(button),100);
Gaurav Yadav
Gaurav Yadav
5,047 Points

okay, I tried that and it works but if its just a matter of giving time to console then why not add a for loop :

const ul = document.querySelector("ul");
const firstListItem = ul.firstElementChild;
console.log(firstListItem);
for(let i=0; i < 10000; i++){
    console.log("A");
}
const button = document.createElement("button");
button.textContent = "I have been added later";
firstListItem.appendChild(button);

This should log out my desired output, but it still logs out the button in li element, moreover, before "A" is logged out 10000 times firstListItem does not log out, there is a space for it in the console but nothing there, as soon as "A" has been logged out 10000 times, that empty space contains the the li element containing button. Why is that happening?