I suggest doing this via HTML in the Browser which is way better than RegEx to read HTML. You do not need to join the DOM but using the Browser is more secure.

Suggestion:

Bring this HTML to a DIV:

var div = document.createElement('div');
div.innerHTML = table;

Put the arrays method into the methods of the nodeLists so you can use querySelectorAll :

NodeList.prototype.filter = Array.prototype.filter;

Use the methods you use in the DOM in this div:

var value = input.value || 0;
var tds = div.querySelectorAll('td');
var match = tds.filter(function (td) {
    return td.innerHTML == value;
});
var resultado = match && match[0].parentNode;
alert(resultado.innerHTML); // vai mostrar só a linha que queres

example: link

EDIT:

Following the clarifications added to the question the final result with my code was to add at the end of this function these lines:

// mark this week
var today = (new Date()).getDate();
var tds = elem.querySelectorAll('td');
NodeList.prototype.filter = Array.prototype.filter;
var match = tds.filter(function (td) {
    return td.innerHTML == today;
});
if (match) match[0].parentNode.style.outline = 'solid 1px red';

jsFiddle: link

EDIT

If the table structure does not really change:

• do not contain tables within tables
• HTML is well formed

Then you can use regex to find the TR opening tag containing the TD with the desired number, as shown in the snippet below:

var num = 8;

var tabela = getTable();

var tabelaSubst = tabela.replace(RegExp("\<\s*tr\s*\>(?=((?!\<\s*\/tr\s*\>).)*\D\s*0*"+num+"\s*\D)", 'g'), "<TR class='achou'>");

document.getElementById("content").innerHTML = (tabelaSubst);

function encodeHtml(rawStr) {
    return rawStr && rawStr.replace(/[\u00A0-\u9999<>\&]/gim, function(i) {
        return '&#' + i.charCodeAt(0) + ';';
    });
}

function getTable() {
    var table = ['<table>' +
        '<tr>' +
        '<td>1</td><td>2</td><td>3</td><td>4</td><td>5</td>' +
        '</tr>' +
        '<tr>' +
        '<td>6</td><td>7</td><td> 08</td><td>9</td><td>10</td>' +
        '</tr>' +
        '<tr>' +
        '<td>11</td><td>12</td><td>13</td><td>14</td><td>15</td>' +
        '</tr>' +
        '<tr>' +
        '<td>16</td><td>17</td><td>18</td><td>19</td><td>20</td>' +
        '</tr>' +
        '</table>'
    ];
    return table[0];
}

.achou {
     color: red;
}

<div id="content"></div>

jsfiddle

OLD: using XML parser

You can use broswer XML parse APIs, and use XPath for this.

What API's are these?

• DOMParser : allows parsing of XML documents (HTML well-formed is XML), and create an AST, which contains the document structure

• Document.evaluate : allows you to search using XPath on an XML document that has been fetched by DOMParser , or even the loaded document, ie the loaded page's own DOM

To support IE8

IE8 does not support the above APIs directly ... but it's possible to use your own:

• ActiveXObject("Microsoft.XMLDOM") allows parsing of XML, besides applying XPath, all using a single object

XPath

This is the default language for querying XML documents. But do not get discouraged by the word Path as XPath is far from being a simple path selector.

Example

function getTrsModernBrowser() {
    var parser = new DOMParser();
    var frag = parser.parseFromString(getTable()[0], "text/xml");
    var xpathResult = frag.evaluate("//tr[td[text()=17]]", frag, null, XPathResult.ANY_TYPE, null);

    var trs = [];
    var result = xpathResult.iterateNext();
    while (result) {
        trs.push(result);
        result = xpathResult.iterateNext();
    }
    return trs;
}

function getTrsIE8() {
    var frag = new window.ActiveXObject("Microsoft.XMLDOM");
    frag.async = "false";
    frag.loadXML(getTable()[0]);
    frag.setProperty("SelectionLanguage", "XPath");
    var results = frag.selectNodes("//tr[td[text()=17]]");
    var trs = [];
    for (it = 0; it < results.length; it++)
        trs.push(results[it]);
    debugger;
    return trs;
}

function getTrs() {
    return window.ActiveXObject ? getTrsIE8() : getTrsModernBrowser();
}

var trs = getTrs();
for (var itTr = 0; itTr < trs.length; itTr++) {
    document.getElementById("content").innerHTML = encodeHtml(
        trs[itTr].outerHTML // browsers que suportam a API DOMParser
        || trs[itTr].xml // IE8
    );
}

function encodeHtml(rawStr) {
    return rawStr && rawStr.replace(/[\u00A0-\u9999<>\&]/gim, function(i) {
        return '&#' + i.charCodeAt(0) + ';';
    });
}

function getTable() {
    var table = ['<table>' +
        '<tr>' +
        '<td>1</td><td>2</td><td>3</td><td>4</td><td>5</td>' +
        '</tr>' +
        '<tr>' +
        '<td>6</td><td>7</td><td>8</td><td>9</td><td>10</td>' +
        '</tr>' +
        '<tr>' +
        '<td>11</td><td>12</td><td>13</td><td>14</td><td>15</td>' +
        '</tr>' +
        '<tr>' +
        '<td>16</td><td>17</td><td>18</td><td>19</td><td>20</td>' +
        '</tr>' +
        '</table>'
    ];
    return table;
}

<div id="content"></div>

jsfiddle, what do you like to play there instead of the SOPT snippet

Dissecting XPath above example

• //tr[td[text()=17]]

• // at beginning instructs the engine to fetch nodes at all levels, not just at the root
• tr is the element to be found, and could be the name of any element
• [ condição ] this operator is an assertion about the previous element, only tr s will be selected with the characteristics defined inside the []
• text()=17 indicates that the text of the element being parsed should be number 17 . Attention to what I said: "THE NUMBER 17" ... will be used numerical comparator. Therefore, the text of the element can be "017", "00017", "17", etc.