java - How to extract text using javascript on client side -

i want develop script extract information client side when enter url our site.

for exmaple-:if enter url www.example.com,the code intiates , extract information client side.it different each user facebook email etc.

so looking @ option , thinking impossible unless have kind of javascript code execute on client side whenever visit site.i looking @ libraries such jsoup,selenium etc guess executes locally , didn't solve purpose.

the text want extract in iframe , further in tables.so possible write code (javascript or else )which include in our index.php page , executes on client site,extract information , store results in database?

the scenario if user logged in facebook on same browser when visit site,it automatically displays email id related facebook.so want extract email id.any suggestions?

edit-->>

i trying following code move frame , content returning empty content document.

var iframe = document.evaluate('//iframe[contains(@src, \"//my.leadpages.net/forms/5620062778032128/5654100301578240/5645914630782976/html/?lp-in-iframe=1\")]',document, null, xpathresult.first_ordered_node_type, null).contentdocument;alert(iframe); 

also if can guide me through how can move frame , it's contents via nodes.iframe has no id,name etc have used xpath way.it detecting frame resulting xpathresult not sure how move , extract text various nodes.this has in javascript.

i'm pretty sure browsers won't let access contents of iframe. thing you're trying achieve sounds smoewhat shady me. why want take data user didn't give explicitly?