How can I replicate something similar to querySelector in browsers like IE 7 and 6?

I've messed around with trying to detect how complex the query is (like if it's just an ID selector, it goes through getElementById instead and s开发者_运维知识库uch) but this is clearly no way to do complex CSS queries and will probably fail on a certain few selectors.

So my question is to anyone who's done something similar, how did you end up replicating it for older browsers.

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Use jQuery? Or at least a selector library like Sizzle. No point in reinventing the wheel.

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For predictable support for wide range of selectors go with Sizzle (or jQuery which uses Sizzle)

Otherwise you could use the snippet from: Creating a querySelector for IE that runs at “native speed” - Ajaxian

if (!document.querySelector)
    document.querySelector = function(selector) {
        var head = document.documentElement.firstChild;
        var styleTag = document.createElement("STYLE");
        head.appendChild(styleTag);
        document.__qsResult = [];

        styleTag.styleSheet.cssText = selector + "{x:expression(document.__qsResult.push(this))}";
        window.scrollBy(0, 0);
        head.removeChild(styleTag);

        var result = [];
        for (var i in document.__qsResult) {
            result.push(document.__qsResult[i]);
        }
        return result;
    }