samedi 28 mars 2020

Why we use "p1Index = -1" and "len=p1.parentNode.childNodes.length"?Please tell me wheater "p1.parentNode.childNodes" point to same thing?

<!DOCTYPE html>
<html>
    <head>
        <title>DOM Range Example</title>
        <script type="text/javascript">
            function useRanges() {
                var range1 = document.createRange(),
                    range2 = document.createRange(),
                    p1 = document.getElementById("p1"),                
                    p1Index = -1,
                    i, len;

                for (i=0, len=p1.parentNode.childNodes.length; i < len; i++) {
                    if (p1.parentNode.childNodes[i] == p1) {
                        p1Index = i;
                       break;
                    }
                }

'

I find it in the javascript for web developer

here we can see p1Index = -1,why we don't use p1Index=0 ? '




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