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zestime/lookahead.js

Created March 13, 2015 10:39
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lookahead.js
> /bbb(?=ccc)/.exec("aaabbbccc") // lookahead
["bbb"]
> /bbb(?=ccc)/.exec("dddbbbeee")
null
> /bbb(?!ccc)/.exec("aaabbbccc") // negative lookahead
null
> /bbb(?!ccc)/.exec("dddbbbeee")
["bbb"]
> /(?<=aaa)bbb/.exec("aaabbbccc") // lookbehind?
Uncaught SyntaxError: Invalid regular expression: /(?<=aaa)bbb/: Invalid group
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