Question

I have a JSON object as follows:

    var jsonObject = {"regex":"<span class=\"Value\">\\$(.+?)<\\/span>"};

My target is to use this regular expression to scrape a value from a html document.

    var match = html.match(new RegExp(jsonObject.regex, 'i'));

This however returns an error. The problem seems to be that the escape sequences in the regex string are lost in the string jsonObject.regex

A call to jsonObject.regex returns

    < span class="Value">\$(.+?)<\ /span>

(The escape sequences like \” and \\ are lost)

I could replace the respective characters using javascript, but it seems the inefficient thing to do since I already have the correct format in the json object.

Any clues or workarounds are appreciated. Thanks!

Answer 1

You are doing two things wrong here.

First and foremost, you are trying to build a program that uses arbitrary regular expressions on HTML. Don’t do that. You have a DOM at your disposal on the client side, you should use one of the selector engines available. Examples include the browser built-in document.querySelectorAll(), Sizzle (which is also part of jQuery), NWMatcher, or an XPath-based selector engine like XPath.js.

Then, you obviously do not use a JSON serializer to build your JSON string on the server side, or things like messed-up escaping would not happen on the client side.

Lastly, what you have in your first code sample is not JSON. It’s a JavaScript object literal. JSON is always a string:

'{"regex":"<span class=\"Value\">\\$(.+?)<\\/span>"}'

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Selecting what you seem to want in jQuery would become as simple as

var value = $("span.value").text();

But as I said, you are not bound to use jQuery, there are lighter-weight alternatives if HTML-scraping is your main goal.