Is javascript appendChild not synchronous

Question

I am deploying a synchronous javascript library in a tag manager, using document.write("<script src=....

Are other methods of adding to the document considered async (for example: document.getElementsByTagName("head")[0].appendChild(script)) when compared to document.write?

It does synchronously append the script node. It does asynchronously load the script. — Bergi, Feb 14 '14 at 05:44
I don't think a question for the *Why* is on-topic here. That's just how it was implemented, and made it into the spec. — Bergi, Feb 14 '14 at 05:45
Related: http://stackoverflow.com/questions/3248384/document-createelementscript-synchronously — Ben, Jan 17 '17 at 02:55

score 0 · Answer 1 · answered Jan 20 '22 at 14:07

appendChild synchronously appends the element to the DOM (Document Object Model).

In your case it synchronously appends the script node, but it asynchronously loads the script, since the script is referenced by its src and hence needs to be loaded via the network. As pointed out by @Bergi.

Had your script been written as content of the script tag then it would have executed entirely synchronously.

let s = document.createElement("script");
s.text = "const myVar = 'hello world'";
document.getElementsByTagName("head")[0].appendChild(s)
console.log(myVar);

will output hello world to the console, thus proving that appendChild is entirely synchronous.

Is javascript appendChild not synchronous

1 Answers1