12 Simple (Yet Powerful) JavaScript Tips

February 20 Last Year

(For Badass JavaScript Development)

NOTICE: I have written only 2 of the 12 tips so far, but I plan to post all 12 Powerful Tips by April 14. This will be a must-read post once all the powerful tips are ready. ;)

I provide you with 12 simple, yet powerful, JavaScript tips and detailed explanation of each. These are techniques that all JavaScript programmers can use now; you needn’t be an advanced JavaScript developer to benefit from these tips. After you read all of the detailed explanations of how each technique works and when to use it, you will have become a more enlightened JavaScript developer, if you aren’t already one.

Indeed, notable JavaScript masters and enlightened JavaScript developers have been using many of these techniques to write powerful, efficient JavaScript. And in a bit, you will, too.

  1. Powerful JavaScript Idiomatic Expressions With && and ||

    You see these idiomatic expressions in JavaScript frameworks and libraries. Let’s start off with a couple of basic examples:

    Example 1: Basic “short circuting” with || (Logical OR)
    To set default values, instead of this:

    function documentTitle(theTitle)
    if (!theTitle) {
      theTitle  = "Untitled Document";
      }
    }

    Use this:

    function documentTitle(theTitle)
      theTitle  = theTitle || "Untitled Document";
    }

    Explanation:
    — First, read the “Important Note” box below for a refresher on JavaScript’s Falsy and Truthy values
    — The || operator first evaluates the expression on the left, if it is truthy, it returns that value. If it is falsy, it evaluates and returns the value of the right operand (the expression on the right).
    — If theTitle variable is falsy, the expression on the right will be returned and assigned to the variable. On the other hand, if theTitle is truthy, its value will be returned and assigned to the variable.

    JavaScript Falsy Values: null, false, 0 undefined, NaN, and “” (this last item is an empty string).
    — Note that Infinity, which is a special number like NaN, is truthy; it is not falsy, while NaN is falsy.

    JavaScript Truthy Values: Anything other than the falsy values.

    Example 2: Basic short circuting with && (Logical AND)
    Instead of this:

    function isAdult(age) {
      if (age && age > 17) {
      return true;
    }
    else {
      return false;
      }
    }

    Use this:

    function isAdult(age) {
       return age && age > 17 ;
    }

    Explanation:
    — The && operator first evaluates the expression on the left. If it is falsy, false is returned; it does not bother to evaluate the right operand.
    — If the the first expression is truthy, also evaluate the right operand (the expression on the right) and return the result.

    It Gets More Exciting!

    Example 3:
    Instead of this:

    if (userName) {
      logIn (userName);
    }
     else {
       signUp ();
    }

    Use this:

     userName && logIn (userName) || signUp ();

    Explanation:
    — If userName is truthy, then call the logIn function with userName as the parameter.
    — If userName is falsy, call the signUp function

    Example 4:
    Instead of this:

    var userID;
    if (userName && userName.loggedIn) {
      userID = userName.id;
    }
    else {
      userID = null;
    }

    Use this:

    var userID = userName && userName.loggedIn && userName.id

    Explanation:
    — If userName is truthy, call userName.loggedIn and check if it is truthy; if it is truthy, then get the id from userName.
    — If userName is falsy, return null.

  2. Powerful Uses of Immediately Invoked Function Expressions

    (How Immediately Invoked Function Expressions Work and When to Use Them)
    IIFE (pronounced “Iffy”) is an abbreviation for Immediately Invoked Function Expression, and the syntax looks like this:

    (function () {
     // Do fun stuff
     }
    )()

    It is an anonymous function expression that is immediately invoked, and it has some particularly important uses in JavaScript.

    How Immediately Invoked Function Expressions Work?

    • The pair of parenthesis surrounding the anonymous function turns the anonymous function into a function expression or variable expression. So instead of a simple anonymous function in the global scope, or wherever it was defined, we now have an unnamed function expression.
    • It is as if we have this:
      
// Shown without the parentheses here:
      ? = function () {};
      
      // And with the parentheses here:
      (? = function () {});
      // An unknown variable assigned the value of a function, wrapped in a parentheses, which turns it into an unnamed function expression.

      Similarly, we can even create a named, immediately invoked function expression:

      (showName = function (name) {console.log(name || "No Name")}) (); // No Name
      
      showName ("Rich"); // Rich
      showName (); // No Name

      — Note that you cannot use the var keyword inside the opening pair of parentheses (you will get a syntax error), but it is not necessary in this context to use var since any variable declared without the var keyword will be a global variable anyway.
      — We were able to call this named function expression both immediately and later because it has a name.
      — But we can’t call the anonymous function expression later, since there is no way to refer to it. This is the reason it is only useful when it is immediately invoked.

    • By placing the anonymous function in parentheses (a group context), the entire group is evaluated and the value returned. The returned value is actually the entire anonymous function itself, so all we have to do is add two parentheses after it to invoke it.
    • Therefore, the last two parentheses tell the JS compiler to invoke (call) this anonymous function immediately, hence the name “Immediately Invoked Function Expression.”

    • Because JavaScript has function-level scope, all the variables declared in this anonymous function are local variables and therefore cannot be accessed outside the anonymous function.
    • So we now have a powerful piece of anonymous code inside an unnamed function expression, and the code is meaningless unless we invoke the anonymous function, because nothing can access the code. It is the immediate invocation of the anonymous function that makes it powerful and useful.
    • You can pass parameters to the anonymous function, just like you would any function, including variables. The anonymous function’s scope extend into any outer function that contains it and to the global scope. Read my article, JavaScript Variable Scope and Hoisting Explained, for more.

    When To Use Immediately Invoked Function Expressions?

    1. To Avoid Polluting the Global Scope
      
The most popular use of the IIFE is to avoid declaring variables in the global scope. Many JavaScript libraries use this technique, and of course many JS pros, too. It is especially popular amongst jQuery plugin developers. And you should use an IIFE in the top-level (main.js) of your applications.

      In this first example, I am using it in the global scope to keep all my variables local to the anonymous function, and thus outside the global scope where variables can shadow (block) other already-defined variables with the same name (probably from an included library or framework). All of my code for the application will start in the IIFE:



       // All the code is wrapped in the IIFE
      (function () {

      var firstName = “Richard”;
      

function init () {
      
  doStuff (firstName);
        // code to start the application
      
}

      
      function doStuff () {
        // Do stuff here
      }
      
      function doMoreStuff () {
       // Do more stuff here
      }
      
      // Start the application

      init ();

      }) ();

      — Note that you can also pass jQuery or any other object or variable via the parameter (the last 2 parentheses).


    2. Use With the Conditional Operator
      The use of the IIFE in this manner is not as well known, but it quite powerful since you can execute complex logic without having to setup and call a named function:

      — Note the two anonymous functions in the conditional statement
      — Why would you do this? Because it is powerful and badass.
      — I purposely added enough space between each section so the code can read better.

      var unnamedDocs = [], namedDocs = ["a_bridge_runover", "great_dreamers"];
      
      function createDoc(documentTitle) {
          var documentName = documentTitle 
      
              ?
      
       (function (theName) {
              var newNamedDoc = theName.toLocaleLowerCase().replace(" ", "_");
              namedDocs.push(newNamedDoc);
      
              return newNamedDoc;
          })(documentTitle)
      
      
              :
      
      
              (function () {
                  var newUnnamedDoc = "untitled_" + Number(namedDocs.length + 1);
                  unnamedDocs.push(newUnnamedDoc);
                  return newUnnamedDoc;
              })();
      
      
          return documentName;
      }
      createDoc("Over The Rainbow"); // over_the rainbow
      createDoc(); // untitled_4
    3. 



    4. Use it in Closures to Prevent Fold Over
      I discussed this particular use of the IIFE before in my post, Understand JavaScript Closures With Ease. So I will copy the section of that code and reuse it here.

      To prevent close over in for loops, we can use an Immediately Invoked Function Expression to prevent a common bug when closures are used with for loops:

      To fix side effects (bug) in closures, you can use an IIFE, such as if this example:

      function celebrityIDCreator (theCelebrities) {
          var i;
          var uniqueID = 100;
          for (i = 0; i < theCelebrities.length; i++) {
              theCelebrities[i]["id"] = function (j)  { // the j parametric variable is the i passed in on invocation of this IIFE
                  return function () {
                      return uniqueID + j; // each iteration of the for loop passes the current value of i into this IIFE and it saves the correct value to the array
                  }
              } (i); // immediately invoke the function passing the i variable as a parameter
          }
      
          return theCelebrities;
      }
      
      var actionCelebs = [{name:"Stallone", id:0}, {name:"Cruise", id:0}, {name:"Willis", id:0}];
      
      var createIdForActionCelebs = celebrityIDCreator (actionCelebs);
      
      var stalloneID = createIdForActionCelebs [0];
      
console.log(stalloneID.id()); // 100
      
      var cruiseID = createIdForActionCelebs [1];
console.log(cruiseID.id()); // 101
Thanks for your time; please come back soon. Email me here: javascriptissexy at gmail email, or use the contact form.

27 Comments

  1. In example 2 the long version also checks callbackFunc, but the short version does not. I think it should be:

    return theTitle & callbackFunc && callbackFunc(theTitle)

    Thanks for writing this blog!

    • Arjan, you’re right but there is a little typo in your code, its must be double and sign between theTitle and callbackFunc, just like this;

      return theTitle && callbackFunc && callbackFunc(theTitle)

      Thank you Arjan and of course Richard by the way.

    • Thanks for pointing that out, Arjan. You are correct, the first example was checking both variables indeed, while the last one was only checking one of the variables.

      I have changed the code to a more practical example.

      And good catch, Rameş.

  2. Pawel

    Hi,

    Yeah, actually i pasted example 4 to console after i defined userName and it doesnt work. I just dont get the logic based on what it should work… its just incorrect.

    “var userID = userName && userName.loggedIn && userName.id”

    will never assign any value other than true/false to the variable, because its a chain of logic coditions, which return either false or true.

    • Hello Pawel, are you sure you didnt forget something while trying code?

      Check this please:
      http://jsbin.com/eladig/1/edit

      • Elsayed Awdallah

        I think it should be
        var userID = userName ? userName.loggedIn : userName.id;
        instead.

        • Elsayed Awdallah

          Sorry for spam but, It’s
          var userID = username && userName.loggedIn ? userName.id : null ;

          • In the example, I am not using the conditional operator, which is what you are using.

            Here are Rameş Aliyev examples, which he has on the jsbin link:

            userName0 = {loggedIn:true, id:5};
            userID0 = userName0 && userName0.loggedIn && userName0.id
            console.log(userID0) // Should print 5

            userName1 = {loggedIn:false, id:5};
            userID1 = userName1 && userName1.loggedIn && userName1.id
            console.log(userID1) // Should print false

            • Nacho Verdón

              Exactly, prints false, but we where expecting null since you said so:

              — If userName is falsy, return null.

              So here is an error.

              I know

              false == null; // true

              but

              fasle === null // false

              null is the value we want, so Pawel was correct. And so is Elsayed except for the little typo on username instead of userName. But those conditionals where not the topic of the post.

              The code we were looking for actually is the one posted by barteks:

              var userID = userName && userName.loggedIn && userName.id || null

    • mjankowski

      Pawel,
      just use the console and see for yourself what a= “b” && “c” does ;-)
      Javascript is a magic language, just google “javascript wat”.

  3. sander

    great tips,
    knew the || but don’t use it enough.
    have never used the && notation for an assignment.

    can’t wait for the other 10.

  4. Addison

    Will you be posting the rest of the tips?

    Looking forward to the rest!!!

  5. Mark

    can’t post, trying a temp shorter post to see if it was my content length

    • Hi Mark, Send me an email with the comment you are trying to post. I know there is an issue with the firewall on the server and I want to fix it.

      I look forward to your reply. Thanks.

  6. Rafique

    Hi,
    This site is awesome to learn JS. 14th April has passed, please I can’t hold myself for another 10 TIPS.

  7. codezyc

    Thank you for sharing this.

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  10. I believe that in Example 4 should be written:
    var userID = userName && userName.loggedIn && userName.id || null to get null if userName or one of it’s property is undefined/ false.

    Best regards,
    Bartek

  11. 123

    For tip 1:
    In example 2 your proposed revision has no more short circuiting than the second one, age > 17 is not evaluated in either if age is falsy. Also, those functions are not equivalent, if age is null the second will return null.

    The code in example 3 is horrible, no one should ever write that. Much better would be
    userName ? logIn (userName) : signUp ();
    because it is far more obvious what is going on without having to remember any operator precedence rules.

  12. rajesh

    Hi Richard,
    Thanks for the article.
    I’m little confused in the statement
    “Because JavaScript has function-level scope, all the variables declared in this anonymous function are local variables and therefore cannot be accessed outside the anonymous function.”
    In the below example

    var a=function(){
    c=20;
    }
    a();
    document.write(c);

    I have declared c in the anonymous function. but i can access this variable globally.

  13. PK

    This website is awesome for learning JavaScript :)
    When are the remaining 10 tips coming.. Can’t wait anymore.

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