Removing leading whitespace from indented HTML source in pre/code tags

The question asks if there’s a JavaScript solution or a simpler method for removing leading whitespace. There’s a simpler method:

CSS

pre, code {
    white-space: pre-line;
}

DEMO

white-space

The white-space property is used to describe how whitespace inside the
element is handled.

pre-line

Sequences of whitespace are collapsed.

To preserve existing whitespace or indentation, each line can be wrapped in a child tag with white-space reset to pre at the line level:

HTML

<pre>
    <code>
        <i>fn main() {</i>
        <i>    println!("hello world!");</i>
        <i>}</i>
    </code>
</pre>

CSS

pre, code {
    white-space: pre-line;
}

pre > code > i {
    white-space: pre;
}