Reverse Engineer Closure Compiled Javascript Code

If you have looked at the javscript source code of Google, you may have noticed that code is not intitutive, like this below code:

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(function(){google.lc=[];google.li=0;google.getEI=function(a){for(var b;a&&(!a.getAttribute||!(b=a.getAttribute("eid")));)a=a.parentNode;return b||google.kEI}; google.getLEI=function(a){for(var b=null;a&&(!a.getAttribute||!(b=a.getAttribute("leid")));)a=a.parentNode;return b}; google.https=function(){return"https:"==window.location.protocol};google.ml=function(){}; google.time=function(){return(new Date).getTime()};google.log=function(a,b,e,f,l){var d=new Image,h=google.lc,g=google.li,c="",m=google.ls||""; d.onerror=d.onload=d.onabort=function(){delete h[g]};h[g]=d;if(!e&&-1==b.search("&ei=")){var k=google.getEI(f),c="&ei="+k; -1==b.search("&lei=")&&((f=google.getLEI(f))?c+="&lei="+f:k!=google.kEI&&(c+="&lei="+google.kEI))} a=e||"/"+(l||"gen_204")+"?atyp=i&ct="+a+"&cad="+b+c+m+"&zx="+google.time();/^http:/i.test(a)&&google.https()?(google.ml(Error("a"),!1,{src:a,glmm:1}), delete h[g]):(window.google&&window.google.vel&&window.google.vel.lu&&window.google.vel.lu(a), d.src=a,google.li=g+1)};google.y={};google.x=function(a,b){google.y[a.id]=[a,b];return!1};google.load=function(a,b,e){google.x({id:a+n++}, function(){google.load(a,b,e)})};var n=0;})();google.kCSI={};

(function(){google.lc=[];google.li=0;google.getEI=function(a){for(var b;a&&(!a.getAttribute||!(b=a.getAttribute("eid")));)a=a.parentNode;return b||google.kEI};
google.getLEI=function(a){for(var b=null;a&&(!a.getAttribute||!(b=a.getAttribute("leid")));)a=a.parentNode;return b};
google.https=function(){return"https:"==window.location.protocol};google.ml=function(){};
google.time=function(){return(new Date).getTime()};google.log=function(a,b,e,f,l){var d=new Image,h=google.lc,g=google.li,c="",m=google.ls||"";
d.onerror=d.onload=d.onabort=function(){delete h[g]};h[g]=d;if(!e&&-1==b.search("&ei=")){var k=google.getEI(f),c="&ei="+k;
-1==b.search("&lei=")&&((f=google.getLEI(f))?c+="&lei="+f:k!=google.kEI&&(c+="&lei="+google.kEI))}
a=e||"/"+(l||"gen_204")+"?atyp=i&ct="+a+"&cad="+b+c+m+"&zx="+google.time();/^http:/i.test(a)&&google.https()?(google.ml(Error("a"),!1,{src:a,glmm:1}),
delete h[g]):(window.google&&window.google.vel&&window.google.vel.lu&&window.google.vel.lu(a),
d.src=a,google.li=g+1)};google.y={};google.x=function(a,b){google.y[a.id]=[a,b];return!1};google.load=function(a,b,e){google.x({id:a+n++},
function(){google.load(a,b,e)})};var n=0;})();google.kCSI={};

(function(){google.lc=[];google.li=0;google.getEI=function(a){for(var b;a&&(!a.getAttribute||!(b=a.getAttribute("eid")));)a=a.parentNode;return b||google.kEI};google.getLEI=function(a){for(var b=null;a&&(!a.getAttribute||!(b=a.getAttribute("leid")));)a=a.parentNode;return b};google.https=function(){return"https:"==window.location.protocol};google.ml=function(){};google.time=function(){return(new Date).getTime()};google.log=function(a,b,e,f,l){var d=new Image,h=google.lc,g=google.li,c="",m=google.ls||"";d.onerror=d.onload=d.onabort=function(){delete h[g]};h[g]=d;if(!e&&-1==b.search("&ei=")){var k=google.getEI(f),c="&ei="+k;-1==b.search("&lei=")&&((f=google.getLEI(f))?c+="&lei="+f:k!=google.kEI&&(c+="&lei="+google.kEI))}a=e||"/"+(l||"gen_204")+"?atyp=i&ct="+a+"&cad="+b+c+m+"&zx="+google.time();/^http:/i.test(a)&&google.https()?(google.ml(Error("a"),!1,{src:a,glmm:1}),delete h[g]):(window.google&&window.google.vel&&
window.google.vel.lu&&window.google.vel.lu(a),d.src=a,google.li=g+1)};google.y={};google.x=function(a,b){google.y[a.id]=[a,b];return!1};google.load=function(a,b,e){google.x({id:a+n++},function(){google.load(a,b,e)})};var n=0;})();google.kCSI={};

1. Prettify

Now the first step is to Prettify the source code. This is what it looks like after using the Prettify tool.

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(function () {   google.lc = [   ];   google.li = 0;       google.getEI = function (a) {     for (var b; a && (!a.getAttribute || !(b = a.getAttribute('eid'))); ) a = a.parentNode;     return b || google.kEI   };       In = function (a, b, c) {     a.ma = c ? Kn(b, !0) : b;   };       Jn = function (a, b, c) {     b instanceof Ln ? (a.$ = b, gra(a.$, a.ga)) : (c || (b = Mn(b, hra)), a.$ = new Ln(b, 0, a.ga));     return a;   };       Nn = function (a) {     return a.$;   };       var n = 0;  }) ();     google.kCSI = {  };

(function () {
  google.lc = [
  ];

  google.li = 0;
  
  google.getEI = function (a) {
    for (var b; a && (!a.getAttribute || !(b = a.getAttribute('eid'))); ) a = a.parentNode;
    return b || google.kEI
  };
  
  In = function (a, b, c) {
    a.ma = c ? Kn(b, !0) : b;
  };
  
  Jn = function (a, b, c) {
    b instanceof Ln ? (a.$ = b, gra(a.$, a.ga)) : (c || (b = Mn(b, hra)), a.$ = new Ln(b, 0, a.ga));
    return a;
  };
  
  Nn = function (a) {
    return a.$;
  };
  
  var n = 0;
 }) ();
 
 google.kCSI = {
 };

Most modern browser support this feature in Developer Tools. Please read here for How to use Prettify Tool.

2. Javascript Debugger:  Apply breakpoints and find HTML events to insert breakpoint.

3. Find the Function Definition

1. Copy the code to Notepad++ IDE.
2. Open the Find tool, Ctrl+ F
3. Set the 'Match case', 'Wrap around' 
4. Set the Search Mode to 'Regular expression' and set the '. matches newline'
5. Insert the below snippet in the 'Find what:'

1	^\s*funcName\s*=\s*function

^\s*funcName\s*=\s*function

    6. Replace the funcName with the name of the function you want to search.

Note:  Escape the character with '\' backslash for special characters like .,_-*+ etc