How to find string using search in java script

I have a string

var str =<useridentifier>=[@ANaccount]

now in above string i want to search   ?<useridentifier>=[@ANaccount]

I have tried using search below
var str1 ="\\?<useridentifier>=[@ANaccount]");

but this one is not working

can u please correct me above code
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Raghu MutalikdesaiSenior Manager in a leading IT Services companyCommented:
Try this way:
var idx = str.indexOf("\\?<useridentifier>=[@ANaccount]");
var str1 = str.substring(idx, str.length - 1);

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mannevenu26Author Commented:
var idx = str.indexOf("\\?<useridentifier>=[@ANaccount]"); not getting value getting idx as -1
Radek BaranowskiFull-stack Java DeveloperCommented:
do it exactly as in

var str = "<useridentifier>=[@ANaccount]";

var check=new RegExp ("[\?<useridentifier>=\[@ANaccount\]]");

//this will output position of "?" for testing purposes
if(check.test(str)==true) alert('\\?'));

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