JavaScript is dynamically typed.
This unassumingly simple feature is one of the most powerful strengths of the language. As your experience with the language evolves you will appreciate the less ceremony involved in creating variables
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| // JAVASCRIPT IS DYNAMICALLY TYPED | |
| var age = 30; | |
| console.log("Age = " + age); // Display's age | |
| console.log("Type of variable age = " + typeof(age)); // Type of variable | |
| console.log("— Dynamically typed —") | |
| age = "new born"; // Proof JavaScript is dynamically typed | |
| console.log("Type of variable age = " + typeof(age)); // Type has changed |
JavaScript has types that are not common in other languages. Type such as “undefined” when operated with number produces NaN (Not a number type), which could be confusing for beginners. To add to the confusion type of NaN is a number thus any arithmetic operation to NaN is never going to throw an exception. More info on variables can be found here.
JavaScript types in action.
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| // Variables declared by default are undefined | |
| console.log("Begin example – 2"); | |
| var x,y = 10; | |
| console.log("Value of x = " + x); // X value is not defined, hence has undefiend | |
| console.log("Value of y = " + y); | |
| // Types demystified | |
| console.log("Type of x = " + typeof(x)); // Type of undefined is undefined. | |
| console.log("–"); | |
| var a=null; | |
| var b=0; | |
| console.log("Value of a = " + a); // a value is null | |
| console.log("Value of b = " + b); | |
| console.log("Type of a = " + typeof(a)); // Type of null is object. | |
| console.log("–"); | |
| var c = a/b; | |
| console.log("Value of c = " + c); | |
| console.log("Type of c = " + typeof(c)); // Type of NaN is number. | |
| console.log("–"); |
Truthy/Falsy explained
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| console.log("Begin example – 3"); | |
| var p = 0; // Try replacing this with null, undefined, NaN | |
| console.log("Value of p = " + p); | |
| console.log("Boolean equivalent of p = " + Boolean(p)); // Truthy or Falsy value | |
| // Example usage of truthy or falsy | |
| if (p){ | |
| console.log("I am happy"); | |
| } else { | |
| console.log("I am not sure"); | |
| } |