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Diffstat (limited to 'javascript.html.markdown')
| -rw-r--r-- | javascript.html.markdown | 128 |
1 files changed, 86 insertions, 42 deletions
diff --git a/javascript.html.markdown b/javascript.html.markdown index 588ea86d..cd75b0d2 100644 --- a/javascript.html.markdown +++ b/javascript.html.markdown @@ -16,13 +16,14 @@ JavaScript isn't just limited to web browsers, though: Node.js, a project that provides a standalone runtime for Google Chrome's V8 JavaScript engine, is becoming more and more popular. -Feedback would be highly appreciated! You can reach me at -[@adambrenecki](https://twitter.com/adambrenecki), or -[adam@brenecki.id.au](mailto:adam@brenecki.id.au). +JavaScript has a C-like syntax, so if you've used languages like C or Java, +a lot of the basic syntax will already be familiar. Despite this, and despite +the similarity in name, JavaScript's object model is significantly different to +Java's. ```js -// Comments are like C. Single-line comments start with two slashes, -/* and multiline comments start with slash-star +// Single-line comments start with two slashes. +/* Multiline comments start with slash-star, and end with star-slash */ // Statements can be terminated by ; @@ -40,7 +41,7 @@ doStuff() // JavaScript has one number type (which is a 64-bit IEEE 754 double). // Doubles have a 52-bit mantissa, which is enough to store integers -// up to about 9✕10¹⁵ precisely. +// up to about 9✕10¹⁵ precisely. 3; // = 3 1.5; // = 1.5 @@ -54,6 +55,11 @@ doStuff() // Including uneven division. 5 / 2; // = 2.5 +// And modulo division. +10 % 2; // = 0 +30 % 4; // = 2 +18.5 % 7; // = 4.5 + // Bitwise operations also work; when you perform a bitwise operation your float // is converted to a signed int *up to* 32 bits. 1 << 2; // = 4 @@ -64,7 +70,7 @@ doStuff() // There are three special not-a-real-number values: Infinity; // result of e.g. 1/0 -Infinity; // result of e.g. -1/0 -NaN; // result of e.g. 0/0 +NaN; // result of e.g. 0/0, stands for 'Not a Number' // There's also a boolean type. true; @@ -104,7 +110,7 @@ null == undefined; // = true // ...unless you use === "5" === 5; // = false -null === undefined; // = false +null === undefined; // = false // ...which can result in some weird behaviour... 13 + !0; // 14 @@ -135,7 +141,7 @@ undefined; // used to indicate a value is not currently present (although // character. var someVar = 5; -// if you leave the var keyword off, you won't get an error... +// If you leave the var keyword off, you won't get an error... someOtherVar = 10; // ...but your variable will be created in the global scope, not in the scope @@ -144,6 +150,10 @@ someOtherVar = 10; // Variables declared without being assigned to are set to undefined. var someThirdVar; // = undefined +// If you want to declare a couple of variables, then you could use a comma +// separator +var someFourthVar = 2, someFifthVar = 4; + // There's shorthand for performing math operations on variables: someVar += 5; // equivalent to someVar = someVar + 5; someVar is 10 now someVar *= 10; // now someVar is 100 @@ -189,8 +199,6 @@ myObj.myFourthKey; // = undefined /////////////////////////////////// // 3. Logic and Control Structures -// The syntax for this section is almost identical to Java's. - // The `if` structure works as you'd expect. var count = 1; if (count == 3){ @@ -218,6 +226,27 @@ for (var i = 0; i < 5; i++){ // will run 5 times } +// The for/in statement iterates over every property across the entire prototype chain. +var description = ""; +var person = {fname:"Paul", lname:"Ken", age:18}; +for (var x in person){ + description += person[x] + " "; +} + +// To only consider properties attached to the object itself +// and not its prototypes, use the `hasOwnProperty()` check. +var description = ""; +var person = {fname:"Paul", lname:"Ken", age:18}; +for (var x in person){ + if (person.hasOwnProperty(x)){ + description += person[x] + " "; + } +} + +// For/in should not be used to iterate over an Array where the index order +// is important, as there is no guarantee that for/in will return the indexes +// in any particular order. + // && is logical and, || is logical or if (house.size == "big" && house.colour == "blue"){ house.contains = "bear"; @@ -231,8 +260,8 @@ var name = otherName || "default"; // The `switch` statement checks for equality with `===`. -// use 'break' after each case -// or the cases after the correct one will be executed too. +// Use 'break' after each case +// or the cases after the correct one will be executed too. grade = 'B'; switch (grade) { case 'A': @@ -262,12 +291,9 @@ myFunction("foo"); // = "FOO" // Note that the value to be returned must start on the same line as the // `return` keyword, otherwise you'll always return `undefined` due to // automatic semicolon insertion. Watch out for this when using Allman style. -function myFunction() -{ +function myFunction(){ return // <- semicolon automatically inserted here - { - thisIsAn: 'object literal' - } + {thisIsAn: 'object literal'} } myFunction(); // = undefined @@ -281,6 +307,12 @@ setTimeout(myFunction, 5000); // Note: setTimeout isn't part of the JS language, but is provided by browsers // and Node.js. +// Another function provided by browsers is setInterval +function myFunction(){ + // this code will be called every 5 seconds +} +setInterval(myFunction, 5000); + // Function objects don't even have to be declared with a name - you can write // an anonymous function definition directly into the arguments of another. setTimeout(function(){ @@ -299,7 +331,7 @@ i; // = 5 - not undefined as you'd expect in a block-scoped language // scope. (function(){ var temporary = 5; - // We can access the global scope by assiging to the "global object", which + // We can access the global scope by assigning to the "global object", which // in a web browser is always `window`. The global object may have a // different name in non-browser environments such as Node.js. window.permanent = 10; @@ -393,7 +425,7 @@ var doubler = product.bind(this, 2); doubler(8); // = 16 // When you call a function with the `new` keyword, a new object is created, and -// made available to the function via the this keyword. Functions designed to be +// made available to the function via the `this` keyword. Functions designed to be // called like that are called constructors. var MyConstructor = function(){ @@ -475,8 +507,9 @@ myNumber === myNumberObj; // = false if (0){ // This code won't execute, because 0 is falsy. } -if (Number(0)){ - // This code *will* execute, because Number(0) is truthy. +if (new Number(0)){ + // This code will execute, because wrapped numbers are objects, and objects + // are always truthy. } // However, the wrapper objects and the regular builtins share a prototype, so @@ -505,28 +538,39 @@ if (Object.create === undefined){ // don't overwrite it if it exists ## Further Reading -The [Mozilla Developer -Network](https://developer.mozilla.org/en-US/docs/Web/JavaScript) provides -excellent documentation for JavaScript as it's used in browsers. Plus, it's a -wiki, so as you learn more you can help others out by sharing your own -knowledge. +The [Mozilla Developer Network][1] provides excellent documentation for +JavaScript as it's used in browsers. Plus, it's a wiki, so as you learn more you +can help others out by sharing your own knowledge. + +MDN's [A re-introduction to JavaScript][2] covers much of the concepts covered +here in more detail. This guide has quite deliberately only covered the +JavaScript language itself; if you want to learn more about how to use +JavaScript in web pages, start by learning about the [Document Object Model][3]. + +[Learn Javascript by Example and with Challenges][4] is a variant of this +reference with built-in challenges. + +[JavaScript Garden][5] is an in-depth guide of all the counter-intuitive parts +of the language. + +[JavaScript: The Definitive Guide][6] is a classic guide and reference book. + +[Eloquent Javascript][8] by Marijn Haverbeke is an excellent JS book/ebook with attached terminal -MDN's [A re-introduction to -JavaScript](https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript) -covers much of the concepts covered here in more detail. This guide has quite -deliberately only covered the JavaScript language itself; if you want to learn -more about how to use JavaScript in web pages, start by learning about the -[Document Object -Model](https://developer.mozilla.org/en-US/docs/Using_the_W3C_DOM_Level_1_Core) +[Javascript: The Right Way][9] is a guide intended to introduce new developers to JavaScript and help experienced developers learn more about its best practices. -[Learn Javascript by Example and with Challenges](http://www.learneroo.com/modules/64/nodes/350) is a variant of this reference with built-in challenges. -[JavaScript Garden](http://bonsaiden.github.io/JavaScript-Garden/) is an in-depth -guide of all the counter-intuitive parts of the language. +In addition to direct contributors to this article, some content is adapted from +Louie Dinh's Python tutorial on this site, and the [JS Tutorial][7] on the +Mozilla Developer Network. -[JavaScript: The Definitive Guide](http://www.amazon.com/gp/product/0596805527/) is a classic guide / reference book. -In addition to direct contributors to this article, some content is adapted -from Louie Dinh's Python tutorial on this site, and the [JS -Tutorial](https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript) -on the Mozilla Developer Network. +[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript +[2]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript +[3]: https://developer.mozilla.org/en-US/docs/Using_the_W3C_DOM_Level_1_Core +[4]: http://www.learneroo.com/modules/64/nodes/350 +[5]: http://bonsaiden.github.io/JavaScript-Garden/ +[6]: http://www.amazon.com/gp/product/0596805527/ +[7]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript +[8]: http://eloquentjavascript.net/ +[9]: http://jstherightway.org/ |