Using JS Objects and Methods

  • In lesson 1.3 discussing data types, we learned how to create objects in JavaScript.
  • Remember that objects store multiple values within one variable, and their values are attributed to their “properties”
  • We can obtain the value of an object’s property by typing the objectName.objectProperty
  • There is a difference between typical variables and objects that we have not yet discussed, and that is the difference between primitive values and reference values.
  • Primitive values are simply values stored to variables without creating new objects.
  • You weren’t aware, but for all of the types of variables we have created so far, there was a way for us to declare those variables as objects.
  • If we were to have declared the variables as objects, they would be of the reference type instead of primitive.
  • For example, lets simply declare a new variable that stores a string of text: 
let primitiveWords = "Have a really great day, like maybe even the best day ever, because why not.";
  • The variable ‘primitiveWords’ is a string primitive.
  • JavaScript identifies six data types as primitive: undefined, null, boolean, number, string, and symbol.
  • That means the following variables are also primitive types:
let year = 2018;
let snowyOutside = false;
let randomVariable;
let placeHolder = null;
  • Now lets create the reference type equivalent of the primitive variable ‘words’:
let referenceWords = new String("Have a really great day, like maybe even the best day ever, because why not.");
  • the variable referenceWords is a String Object.
  • The purpose of learning about the difference between primitive and reference types is to understand the use of JavaScript methods.
  • JavaScript methods exist for the different objects in the JavaScript library.
  • An object’s method is essentially a function that was programmed as a property of that object, and therefore we can invoke the function similarly to how we retrieve any property of an object: objectName.objectMethod()
  • We have not yet covered functions, so we will not learn about writing object methods until the next section.
  • Instead, this lesson focuses on using the objects methods already built into the JavaScript library.
  • Lets start with the String Object and its methods:
  • As you saw, we can create a reference type variable that stores a string object.
  • On this object, we can use the methods created for JavaScript String Objects, such as:
    • .length : returns the length of a string
    • .indexOf(“word”) : returns the index of the first occurrence of the specified text within quotes
    • .slice(start, end) : splits a string into two strings, the new string containing the text within the start and end indexes
  • For example: 
console.log(referenceWords.length); // this prints 76 to the console
console.log(referenceWords.indexOf("great")); // this prints 14 to the console
console.log(referenceWords.indexOf("why")); // this prints 68 to the console
  • However, if I try to use these methods with the primitiveWords variable….
console.log(primitiveWords.length); // this prints 76 to the console
console.log(primitiveWords.indexOf("great")); // this prints 14 to the console
console.log(primitiveWords.indexOf("why")); // this prints 68 to the console
  • The methods still work even though primitiveWords is a primitive type!!!
  • This is because, whenever these methods are invoked, JavaScript treats primitive values as objects in order to use the many methods in the JS library.
  • This means that we can apply the JavaScript methods for most objects to their primitive equivalent.
  • We will now cover a few different methods and objects from JavaScript’s library

Exercises

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