ten groovy little javascript tips

Ten Groovy Little JavaScript TipsSo Cal Code Camp, July 28, 2013

Thursday, July 25, 13

Who am I?Hi, I’m Troy. I have been developing software for over 30 years. For the last 10 years I have been focused on web, mobile web, and mobile development. I currently work at Kelley Blue Book as a senior software engineer. My opinions are my own.

I can be reached rockncoder@gmail.com

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The Rock n Coder

• http://therockncoder.blogspot.com

• http://www.youtube.com/user/rockncoder

• https://github.com/Rockncoder

• http://www.slideshare.net/rockncoder

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The Browser Wars

• ActionScript

• Java

• JavaScript

• JScript

• VBScript

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The browser wars are over.

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JavaScript won.

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Get used to it.

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Get better at it.

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Our Goal

To provide you with some simple to follow, easy to remember tips, which can improve your JavaScript.

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The Tips

• Code

• Conditionals

• Conversions

• jQuery

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Code

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Tip #1Use protection

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Use Protection

• The Browser is a very dirty environment

• Protect your code by wrapping it in a function

/* using protection */ (function (doc, win) { /* put all of your precious code here to keep it safe */ /* extra bonus, parameters passed in become local, minor performance boost */ }(document, window));

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Tip #2debugger is your friend

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debugger is your friend• At times it can be difficult to set a

breakpoint

• The debugger statement allows you to set a breakpoint any where you like

app.post("/clientadmin", function (req, res) { var clientId = req.body.client; console.log("/clientadmin POST: " + JSON.stringify(req.body)); if (clientId) { mongodb.getClientModel().findOne({_id: clientId }, function (err, client) { mongodb.getCampaignModel().find({clientId: clientId}, function (err, campaigns) { debugger; console.log("Campaigns: " + JSON.stringify(campaigns)); /* set the client id */ res.cookie('clientId', clientId); res.cookie('client', JSON.stringify(client)); res.render("clientadmin.hbs", {client: client, campaigns: campaigns, user: extractUser(res)}); }); }); } });

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Conditionals

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Tip #3Always Use ===

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Always Use ===

• Double equals (==) does automatic type conversion

• The results of this conversion is not logical or obvious

• Avoid this by using triple equals (===)

• There is no good reason to ever use ==

• Same goes for !=

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Tip #4Learn to love falsey

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Learn to Love Falsey

• When coming from C# or Java it is tempting to use C-like conditionals

• JavaScript conditionals can be more succinct and performant

1 /* C-style conditional */ 2 if (val != null && val.length > 0){ 3 ... 4 } 5 6 /* JavaScript style conditional */ 7 if (val) { 8 ... 9 }10

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Falsey

Type Results

Null FALSE

Undefined FALSE

Number if 0 or NaN, FALSE

String if length = 0, FALSE

Object TRUE

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Conversions

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JavaScript’s Conversion Shortcuts

• Default Value

• To Binary

• To Number

• To String

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Tip #5Getting default value

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Getting a default value

• At times it is nice to have a default value

• JavaScript has a kind of default value operator /* Conversions */ var defaultValue = defaultValue || 16; var defaultString = inputValue || “Here is the default value”; console.log(defaultValue);

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Tip #6Convert to boolean

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To Binary

• Double exclamation (!!) converts a value to its boolean representation (true/false)

/* convert to boolean */ var toBinary = !!null; console.log(toBinary);

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Tip #7Convert string to

number

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To Number

• The plus sign (+) before a numeric string converts it to a numeric value

/* convert to number */ var toNumber = +"42"; console.log(toNumber);

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Tip #8Convert value to string

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To String

• Add an empty string (“”) to a value converts it to a string

var toString = 42 + ""; console.log(toString);

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jQuery

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Tip #9jQuery isn’t always the

answer

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jQuery Isn’t Always the Answer

• For many tasks plain JavaScript is better than jQuery

• For example, finding an element by its id, jQuery calls document.getElementById()

/* get element by Id is faster than... */ var el = document.getElementById("myDiv"); /* $('#myDiv'), which calls it */ var $el = $('#myDiv').eq(0);

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Tip #10Cache Selectors

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Cache Selectors

• jQuery Selectors are method calls, not operators

• The method calls interrogate the DOM

• Method calls are slow

• Interrogating the DOM is VERY slow

• Caching selectors can dramatically improve the speed of your code

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Cache Selectors/* jQuery Demo */ RocknCoder.plugInSlow = function() { var i, val; for(i=0; i < 50; i++) { val = $('#styleMe').html(); } } RocknCoder.plugInFast = function() { var i, val, $styleMe = $('#styleMe'); for(i=0; i < 50; i++) { val = $styleMe.html(); } }

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Bonus Tip #1Use

event.preventDefault

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Use event.preventDefault• If your code completely handles an event,

you should be sure to event.preventDefault

• This will stop unnecessary code from executing

$('#usRank').on('click', function(evt){ evt.preventDefault(); showChart('US Rank', filterUSRank); });

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Summary

• JavaScript is the most important language of web development

• But it is a quirky language

• Use these tips to speed up your code

• And make your JavaScript code groovier

Thursday, July 25, 13

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Thursday, July 25, 13