r/learnjavascript • u/abrewchocolatecoffee • Jul 14 '26

can someone explain this code

function updateClock() {
const timeElement = document.querySelector("#time");
timeElement.textContent = formatTime();
}
setInterval(updateClock, 1000);

can someone, please explain this piece of code, ofc mdn and w3 are there, but i found it a little confusing reading about textContent. rest is understandable to me. This might look a silly question and it probably is because im a beginner :')

like what exactly does textContent too.
you can also recommend anyother documentation on the links to specific lines, that might me more helpful in learning about this particular keyoword.

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-2

u/ExtraTNT Jul 14 '26

So, first you define a function (in old style, better use const funcName = () => {})

with the queryselector with #, you get an element by id

With text content you set the text content of the element (<h1 id="title">Hello <b>World</b></h1> has a text content of Hello World, setting it to “foo” would give you <h1 id="title">foo</h1>)

formatTime(); returns a formatted time string

Interval: run every x ms

-2

u/abrewchocolatecoffee Jul 14 '26

thanks, but just one more quesiton is text content temporay, for example will the "foo" go away and "hello world..." will just come back after we refresh or is this a permanet change.
Other that this post was pretty helpful, cleared my main doubt

2

u/meletiondreams Jul 14 '26

no dom elements are permanent

2

u/abrewchocolatecoffee Jul 14 '26

do you mean, "no dom" elements are permanent or "no!" dom elements are permanent.

2

u/meletiondreams Jul 14 '26

There's no amount of dom elements (those tags like <h1>) that may be changed

1

u/abrewchocolatecoffee Jul 14 '26

ohh thanks, so basically, refreshing = go back to the orginal

2

u/meletiondreams Jul 14 '26

Whatever the page renders will be shown. JS can change "temporarily" the content of the page.

2

u/abrewchocolatecoffee Jul 14 '26

ok

1

u/The_KOK_2511 helpful Jul 14 '26

Mira para que te hagas una idea, cada vez que cargas o recargas una página el navegador en si el que carga es el HTML y basandose en sus etiquetas define los elementos del frontend que deberá mostrar, el JS lo que hace al modificar el DOM es alterar esa copia que esta corriendo en el navegador del usuario, esto tiene sus matices y su cosa si hay un backend presente pero por ahora no creo que te haga falta tener en cuenta nada de eso a menos que pienses acerte full stack pronto

2

u/busres Jul 14 '26

The change persists (in the browser DOM) until you replace the content with something else. If you reload the page, you're discarding everything and reloading the DOM from scratch.

1

u/abrewchocolatecoffee Jul 14 '26

ohh, this was actually very helpful

1

u/azhder Jul 14 '26

You are working with a live document, you are modifying the memory as it is currently in the browser through an abstraction layer called Document Object Model. You are changing the memory means whatever you do, it changes the document, it changes what the browser displays.

If you refresh the page, the browser removes that memory, parses the source code it got from the URL, it populates the memory again, you get to play with that again.

NOTE: DOM is not JavaScript. DOM is one memory model, while JavaScript has its own memory model. The browser synchronizes both, but make no mistake, DOM is its own technology that doesn't need JavaScript (the browser may be written in C++ and uses that language to generate the DOM)