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Using typeof in a Real-World Scenario One interesting aspect of looking at everything as an object in JavaScript has to do with creating custom functions. This is something I mention in my jquery tutorial book all the time. Let’s say we want to write a function. Then, based on the type of an object passed to this function as an argument we want to do something different. The typeof function to the rescue: function func(value) { if (typeof(value) == “string”) { // it’s a string, process the string... } if (typeof(value) == “object”) { // it’s an object... } } But who would want to do it this way and why? The idea is actually utilized by jQuery object. Which is the same as the dollar sign $ object. Let’s take a look at the following jQuery code: Both functions do exactly the same thing - they select all div elements on the page located within the body element (which means all of them) and hide them. As you may know the second parameter of the jQuery object function we are seeing here is called context. The context parameter is nothing more than the target element within which we will search for any “div” elements. I chose “body” which is the main HTML container of the entire web page. We could have chosen any other element - that’s up to your site’s DOM structure. But that’s not the point of this example. The difference is in the parameter type passed to the function. What happens when a string is passed? What happens when an object is passed? The $(“body”) statement itself returns the object that contains the DOM that includes all elements within the “body” element. 57
Why does jQuery do exactly the same thing even though the second parameter passed in two different ways? The typeof function to the rescue. The jQuery function written in such a way that it first determines the type of the object being passed to it as a parameter. If the context parameter is a string like “body” it will take its literal meaning and find that element using the text in the string. If the parameter is passed as an object (remember that $(“body”) is a function that actually returns an object) then the work is already done - we already have the object here. Internally, the $ function will skip the seeking algorithm (since the object already contains all the data.) This doesn’t mean that it’s faster, $(“body”) will still take time to obtain the object itself, it’s just that it’s done before this object is passed to the main jQuery function for processing. 58
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“ Second Revision. July 2012 Unde
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Prototype, JavaScript Objects and J
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Thought transcends matter. When we
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Preface The purpose of this book is
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A Lesson in Creativity The web deve
Page 11 and 12: I love jQuery because it allows me
Page 13 and 14: Improving Page Load Performance The
Page 15 and 16: Determining the Placement of Intern
Page 17 and 18: JavaScript 1. The only language peo
Page 19 and 20: What is JavaScript? Web designers u
Page 21 and 22: As you can see, variables can be as
Page 23 and 24: The example above will first execut
Page 25 and 26: Only variables and events should be
Page 27 and 28: Notice that variables a and b are c
Page 29 and 30: What Exactly is a JavaScript Variab
Page 31 and 32: A variable allocates enough data st
Page 33 and 34: Do you want to really understand pr
Page 35 and 36: What is a Variable? Variables can b
Page 37 and 38: In order to understand bitwise logi
Page 39 and 40: At first this might seem confusing.
Page 41 and 42: Let’s display the variable “a
Page 43 and 44: What’s important is the return va
Page 45 and 46: Inserting Form Values into MySQL Da
Page 47 and 48: I like code that you can “read”
Page 49 and 50: An object is created from a class.
Page 51 and 52: Dynamic Prototype-based Objects in
Page 53 and 54: Without knowing anything at all abo
Page 55 and 56: More About JSON JSON is a data inte
Page 57 and 58: In some programming languages the t
Page 59 and 60: JavaScript from scratch. If you are
Page 61: property access operator - the . (d
Page 65 and 66: Learning jQuery The greatest thing
Page 67 and 68: If this sounds like you, then you w
Page 69 and 70: Web App Initialization To initializ
Page 71 and 72: In JavaScript, we can define variab
Page 73 and 74: As mentioned above, to an experienc
Page 75 and 76: Including jQuery In Your Source Cod
Page 77 and 78: Including jQuery as an External CDN
Page 79 and 80: Including jQuery UI In the Starting
Page 81 and 82: What Kind of Elements Can You Selec
Page 83: To traverse the DOM and make sure t
Page 86 and 87: Here is a basic inline CSS example
Page 88 and 89: Because the DIV element has ID of
Page 90 and 91: After selecting all of these input
Page 92 and 93: Figure 1 Mentality of a beginner jQ
Page 94 and 95: Whose Children Are These? If we are
Page 96 and 97: Next, let’s explore the possibili
Page 98 and 99: jQuery Events Because jQuery is so
Page 100 and 101: Of course, the effects of binding a
Page 102 and 103: Using toggle() Events Toggling betw
Page 104 and 105: Speed Up Your jQuery Code jQuery is
Page 106 and 107: Let’s now look at the jQuery way
Page 108 and 109: Practical jQuery Lessons Instead of
Page 110 and 111: There is a solution to this problem
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jQuery provides a secondary way of
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Lesson 3: Callback Functions All jQ
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For example, the following statemen
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As you may know an object can conta
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Notice that when we do it this way,
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Alternatively, we can create the pa
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if (“light”.match(/darkness/) =
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jQuery and Regular Expressions In p
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This is probably as simple as it ge
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The following example will demonstr
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Making Good CSS Buttons This tutori
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Sometimes it makes sense to make th
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1. Specify javascript: return false
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Our goal is to match the button wit
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So far, we have briefly discussed t
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Note from the Author Looks like you
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