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Table of Contents

JavaScript Enlightenment

Preface

1. JavaScript Objects

Creating Objects

JavaScript Constructors Construct and Return Object Instances

The JavaScript Native/Built-In Object Constructors

User-Defined/Non-Native Object Constructor Functions

Instantiating Constructors Using the new Operator

Creating Shorthand/Literal Values from Constructors

Primitive (a.k.a. Simple) Values

The Primitive Values null, undefined, “string”, 10, true, and false Are Not Objects

How Primitive Values Are Stored/Copied in JavaScript

Primitive Values Are Equal by Value

The String, Number, and Boolean Primitive Values Act Like Objects When Used Like Objects

Complex (a.k.a. Composite) Values

How Complex Values Are Stored/Copied in JavaScript

Complex Objects Are Equal by Reference

Complex Objects Have Dynamic Properties

The typeof Operator Used on Primitive and Complex Values

Dynamic Properties Allow for Mutable Objects

All Constructor Instances Have Constructor Properties that Point to Their Constructor Function

Verify that an Object Is an Instance of a Particular Constructor Function

An Instance Created From a Constructor Can Have Its Own Independent Properties (Instance Properties)

The Semantics of “JavaScript Objects” and “Object() Objects”

2. Working with Objects and Properties

3. Object()

4. Function()

5. The Head/Global Object

6. The this Keyword

7. Scope and Closures

8. Function Prototype Property

13. Working with Primitive String, Number, and Boolean Values

The Primitive Values null, undefined, “string”, 10, true, and false Are Not Objects

The null and undefined values are such trivial values that they do not require a constructor function, nor the use of the new operator to establish them as a JavaScript value. To use null or undefined, all you do is use them as if they were an operator. The remaining primitive values string, number, and boolean, while technically returned from a constructor function, are not objects.

Below, I contrast the difference between primitive values and the rest of the native JavaScript objects.

Live Code

<!DOCTYPE html><html lang="en"><body><script>

/* no object is created when producing primitive values, 
notice no use of the "new" keyword */
var primitiveString1 = "foo";
var primitiveString2 = String('foo');
var primitiveNumber1 = 10;
var primitiveNumber2 = Number('10');
var primitiveBoolean1 = true;
var primitiveBoolean2 = Boolean('true');

// confirm the typeof is not object
console.log(typeof primitiveString1, typeof primitiveString2); 
  // logs 'string,string'
console.log(typeof primitiveNumber1, typeof primitiveNumber2); 
  // logs 'number,number,
console.log(typeof primitiveBoolean1, typeof primitiveBoolean2); 
  // logs 'boolean,boolean'

// versus the usage of a constructor and new keyword for creating objects

var myNumber = new Number(23);
var myString = new String('male');
var myBoolean = new Boolean(false);
var myObject = new Object();
var myArray = new Array('foo', 'bar');
var myFunction = new Function("x", "y", "return x * y");
var myDate = new Date();
var myRegExp = new RegExp('\\bt[a-z]+\\b');
var myError = new Error('Crap!');

// logs 'object object object object object function object function object'
console.log(
typeof myNumber,
typeof myString,
typeof myBoolean,
typeof myObject,
typeof myArray,
typeof myFunction, // BE AWARE typeof returns function for all function objects
typeof myDate,
typeof myRegExp, // BE AWARE typeof returns function for RegExp()
typeof myError
);

</script></body></html>

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Contents

1. JavaScript Objects > The Primitive Values null, undefined, “string”, 10, tru...

The Primitive Values null, undefined, “string”, 10, true, and false Are Not Objects