Beginner's Guide to Javascript You Should Know For AdWords Scripts

I've heard from a few readers that the posts on this blog have inspired them to learn to code. That's awesome! But I've also heard from a few that say they have run into trouble getting through many of the Javascript tutorials out there since they deal mostly with Javascript for web design or Node.js.

So this post is going to attempt to get someone up to speed with Javascript enough that they can at least walk through most of the code I post here and make changes when needed. Also, I aim to at least help you know what to Google when you get stuck.

A few caveats. Is this meant to be a replacement for a full coding class? No. Will I be making generalizations and over-simplifying some extremely complex topics? Yes. Are there mistakes in this? Probably. If you find one, let me know.

/*********************************
* Intro to Javascript For AdWords Scripts
* Version 1.0
* Created By: Russ Savage
* FreeAdWordsScripts.com
*********************************/
function main() {
  // This is a comment. AdWords Scripts ignores this
  /* Here is another way to comment
     that can be used when you need
     to comment multiple lines */
  
  // The main function tells AdWords where to start. You always need
  // at least a main function in your script.
  
  // Let's start with some variables (or primatives)
  // More info on Javascript variables can be found:
  // http://www.tutorialspoint.com/javascript/javascript_variables.htm
  var clubName = 'Fight Club'; // declared with single quotes
  var rule1 = "Don't talk about fight club."; // or double quotes if needed
  var members = 12; // a number, no quotes
  var dues = 3.50; // also a number
  var isAcceptingNewMembers = true; // a boolean, for yes or no answers
  
  // When you need to store multiple values, consider an Array
  // More detailed intro to Arrays can be found here:
  // http://www.w3schools.com/js/js_obj_array.asp
  var memberNames = ['brad','edward','robert'];
  // Which you can access the values with an index
  var coolestMember = memberNames[0]; // pronounced member names sub zero
  // 0 is the index of the first element of the array, 1 for the second, etc.
  // We can use the length property of an array to find out how big it is.
  var numberOfMembers = memberNames.length; // this will be 3
  var dailyFights = numberOfMembers*2; // star ( * ) is an operator for multiply
  // so the total number of fights is 6.
  // More on operators can be found here:
  // http://web.eecs.umich.edu/~bartlett/jsops.html
  
  // If you want to group multiple variables together, you can using an Object.
  // An Object is simply a grouping of common variables (and other stuff we'll see later)
  var FightClub = { // The curly brace says group these things together. there is another one at the end.
    clubName : 'The Fight Club', // a string variable. In an Object, we use : instead of = for assignment
    rules : ["Don't talk about fight club.",  // each variable is separated by a comma, instead of a semi-colon
             'Do not talk about fight club.'],
    memberNames : ['brad','eddy','robert','phil','dave'],
    dues : 3.50, 
    foundedYear : 1999
  };
  // Now to access the variables inside the object, we use the dot
  Logger.log(FightClub.clubName); // prints The Fight Club
  Logger.log(FightClub.memberNames[0]); // prints brad
  
  // Objects are one of the most important concepts of Javascript and they will come back
  // again and again a little later. More details can be found here:
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects
  
  // Sidebar: Why do I use camelCase for variable names? Technically
  // I could 
  var UsEWhaTevERIwanteD = 'but camelCase is easier to read';
  // and conforms to the style guide that Google recommends:
  // https://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml#Naming
  // Follow the style guide. It helps others read your code.
  
  // If statements (or control statements) allow you to split your code path if needed
  if(numberOfMembers > 10) { // if we have more than 10 members
    dues += 1.00; // increase the dues, 
    // plus equals (+=) says "add the value on the right to the value on the left"
  } else { // otherwise
    dues -= 1.00; // decrease the dues
    // there are also -=, *= (multiply), /= (divide by), and %= (modulo equals)
  }
  // Comparison operators like >, <, ==, ===, <=, >= allow you to compare values
  // They return true or false, always
  // Notice the double and triple equal signs. That's not a typo. More info can be found at:
  // http://www.impressivewebs.com/why-use-triple-equals-javascipt/
  
  // You can also have multiple if statements and multiple things to test
  if(dues > 5) { // if dues are over $5
    dailyFights++; // increase the fights
  } else if(dues > 2 && dues <= 5) { // if dues are greater than $2, but less than $5
    dailyFights--; // decrease the fights
  } else { // otherwise
    dailyFights = numberOfMembers*2; // reset the fights
  }
  // You'll probably notice none of this makes sense. it is only for example.
  // Double Ampersand && just means AND, || means OR. So in the statement above,
  // both statements with operators must be true in order for the fights to be decreased.
  // Oh, and ++, -- is shortcut for +=1 and -=1 respectively.
  
  // Ok, now lets talk about loops. 
  // Here are a few different ways to loop through the members
  // This is called a While Loop and while it might be easy to understand,
  // You won't use it nearly as often as the other two.
  var i = 0; // the variable i is what we will use for each indice
  while(i < memberNames.length) { // while i is less than the length of names
    Logger.log(memberNames[i]); // print out the name
    i++; // and increment the index by 1
  }
  // i is a variable that controls the loop. A common issue with While loops
  // is that you will forget to increment the loop control and you get an infinate loop
  
  // This is the classic For loop
  // The declaration, checking, and incrementing are all done 
  // in the first line so it is harder to miss them
  for(var index = 0; index < memberNames.length; index++) {
    Logger.log(memberNames[index]);
  }
  
  // And finally, the easiest loop but hardest to explain, the ForEach loop
  // This is just a variation of the For loop that handles incrementing index
  // behind the scenes so you don't have to.
  for(var index in memberNames) { // declare index, which will be assigned each indice
    Logger.log(memberNames[index]); // Use the indice to print each name
  }
  
  // You can jump out of a loop before it reaches the end by combining the if statement
  for(var index in memberNames) { 
    if(memberNames[index] === 'edward') {
      break; // break is a keyword you can use to break out of the loop.
    }
    Logger.log(memberNames[index]); 
  }
  // In this case, only the first name is printed because we broke out once we had the 
  // second name. More on break and its partner, continue, check out:
  // http://www.tutorialspoint.com/javascript/javascript_loop_control.htm
  
  // Now let's talk about functions. We have already seen a function in action: main()
  // Functions are groupings of useful code that you can call over and over again easily
  function fight(player1, player2) {
    if(Math.random() < .5) {
      return player1;
    } else {
      return player2; // return means we are going to send player2 back 
                      // to the code that called the function
    }
  }
  // This code can be called over and over again using a loop
  for(var player1 in memberNames) { // Loop through each member
    for(var player2 in memberNames) { // Then loop through again 
      if(player1 !== player2) { // Players can't fight themselves so check for that
        Logger.log(fight(player1,player2)); // Then call the function we defined earlier
      }
    }
  }
  // This code calls fight() for:
  //    brad vs. edward, brad vs. robert
  //    edward vs. brad, edward vs. robert
  //    robert vs. brad, robert vs. edward
  // Some other functions we have been calling are Logger.log() and Math.random()
  // The cool thing is that as callers of the function, we only need to know how
  // to call the function, we don't need to know how it works behind the scenes
  // For example:
  //   var answer = LargeHadronColider.simulateEleventhDimensionalQuantumThingy(47);
  // Who knows how this works. All we need to know is to send it a number and expect a
  // number back.
  
  // I hope you've been noticing all of the Objects we have been using here. Logger is one,
  // Math is another one (and LargeHadronColider is a fake one). Along with variables, we 
  // can also put functions in there as well:
  var FightClub = { 
    // ... all that other stuff
    chant : function() { 
      Logger.log('His name is Robert Paulson.'); 
    },
    totalMembers : 5
  };
  // Whoa trippy. So what happens when I call 
  FightClub.chant();
  // It's going to print His name is Robert Paulson
  
  // The thing that makes Google AdWords Scripts different from writing just regular Javascript
  // is all of the pre-defined Objects that use functions to interact with AdWords.
  AdWordsApp.currentAccount();
  Utilities.jsonParse('{}');
  AdWordsApp.keywords().withLimit(10).get();
  // How does the above statement work?
  AdWordsApp  // this is a predefined object in AdWords Scripts
    .keywords() // which has a function called keywords() that returns a KeywordSelector object
    .withLimit(10) // which has a function withLimit() that returns the same KeywordSelector object
    .get(); // which has a function get() that returns a KeywordIterator object.
  // Check out the AdWords Scripts documentation to find the objects and classes that make up these calls
  // https://developers.google.com/adwords/scripts/docs/reference/adwordsapp/adwordsapp
  // https://developers.google.com/adwords/scripts/docs/reference/adwordsapp/adwordsapp#keywords_0
  // https://developers.google.com/adwords/scripts/docs/reference/adwordsapp/adwordsapp_keywordselector
  // https://developers.google.com/adwords/scripts/docs/reference/adwordsapp/adwordsapp_keywordselector#withLimit_1
  // https://developers.google.com/adwords/scripts/docs/reference/adwordsapp/adwordsapp_keywordselector#get_0
  
  // So I think that just about does it for this tutorial.  If you made it this far, awesome! Post a comment to ask
  // any questions you might have.
  
  // Thanks,
  // Russ
}