var paragraphs = document.getElementsByTagName("p");
for (var i = 0; i < paragraphs.length; i++) {
    var paragraphValue = paragraphs[i].textContent;
    console.log(paragraphValue);
}

$("p").each(function() {
    var paragraphValue = $(this).text();
    console.log(paragraphValue);
});

var html = "<p>第一个段落</p><p>第二个段落</p><p>第三个段落</p>";
var regex = /<p>(.*?)<\/p>/g;
var match;
while ((match = regex.exec(html)) !== null) {
    var paragraphValue = match[1];
    console.log(paragraphValue);
}