Update URL parameter

I have the following string:

http://www.website.com?a=11开发者_StackOverflow中文版1&b=2222&d=3333

How can I take this string and update the b parameter value with 4444?

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var str = 'http://www.website.com?a=111&b=2222&d=3333';
str.replace(/([&\?]b=\d+/,"$1b=4444")

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String.replace(/b=([^&]*)/, "b=4444")

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var myString = "http://www.website.com?a=111&b=2222&d=3333".replace("b=2222","b=4444")