What's wrong with my Javascript regex?

I would like regex to match if and only if the string is none, family or work (but not my family开发者_运维知识库, for example).

Why the following code results with "match" ? Why ^ and $ do not work ?

var regex = new RegExp("^none|family|work$");
var str = "my family";
document.write(regex.test(str) ? "match" : "no");

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The | operator has low precedence, so you effectively have (^none)|(family)|(work$), which matches anything beginning with none, containing family or ending with work.

Use this instead:

^(none|family|work)$

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Your regex matches either:

• “none” at the beginning of the string;
• “family” anywhere in the string; or
• “work” at the end of the string.

What you probably want instead is

var regex = new RegExp("^(none|family|work)$");