diff options
Diffstat (limited to 'javascript.html.markdown')
| -rw-r--r-- | javascript.html.markdown | 93 |
1 files changed, 51 insertions, 42 deletions
diff --git a/javascript.html.markdown b/javascript.html.markdown index 7c869b28..588ea86d 100644 --- a/javascript.html.markdown +++ b/javascript.html.markdown @@ -39,13 +39,14 @@ doStuff() // 1. Numbers, Strings and Operators // JavaScript has one number type (which is a 64-bit IEEE 754 double). -// As with Lua, don't freak out about the lack of ints: doubles have a 52-bit -// mantissa, which is enough to store integers up to about 9✕10¹⁵ precisely. +// Doubles have a 52-bit mantissa, which is enough to store integers +// up to about 9✕10¹⁵ precisely. 3; // = 3 1.5; // = 1.5 -// All the basic arithmetic works as you'd expect. +// Some basic arithmetic works as you'd expect. 1 + 1; // = 2 +0.1 + 0.2; // = 0.30000000000000004 8 - 1; // = 7 10 * 2; // = 20 35 / 5; // = 7 @@ -77,13 +78,13 @@ false; !true; // = false !false; // = true -// Equality is == -1 == 1; // = true -2 == 1; // = false +// Equality is === +1 === 1; // = true +2 === 1; // = false -// Inequality is != -1 != 1; // = false -2 != 1; // = true +// Inequality is !== +1 !== 1; // = false +2 !== 1; // = true // More comparisons 1 < 10; // = true @@ -97,25 +98,31 @@ false; // and are compared with < and > "a" < "b"; // = true -// Type coercion is performed for comparisons... +// Type coercion is performed for comparisons with double equals... "5" == 5; // = true +null == undefined; // = true // ...unless you use === "5" === 5; // = false +null === undefined; // = false -// You can access characters in a string with charAt +// ...which can result in some weird behaviour... +13 + !0; // 14 +"13" + !0; // '13true' + +// You can access characters in a string with `charAt` "This is a string".charAt(0); // = 'T' -// ...or use substring to get larger pieces +// ...or use `substring` to get larger pieces. "Hello world".substring(0, 5); // = "Hello" -// length is a property, so don't use () +// `length` is a property, so don't use (). "Hello".length; // = 5 -// There's also null and undefined -null; // used to indicate a deliberate non-value +// There's also `null` and `undefined`. +null; // used to indicate a deliberate non-value undefined; // used to indicate a value is not currently present (although - // undefined is actually a value itself) + // `undefined` is actually a value itself) // false, null, undefined, NaN, 0 and "" are falsy; everything else is truthy. // Note that 0 is falsy and "0" is truthy, even though 0 == "0". @@ -123,8 +130,9 @@ undefined; // used to indicate a value is not currently present (although /////////////////////////////////// // 2. Variables, Arrays and Objects -// Variables are declared with the var keyword. JavaScript is dynamically typed, -// so you don't need to specify type. Assignment uses a single = character. +// Variables are declared with the `var` keyword. JavaScript is dynamically +// typed, so you don't need to specify type. Assignment uses a single `=` +// character. var someVar = 5; // if you leave the var keyword off, you won't get an error... @@ -158,7 +166,7 @@ myArray.length; // = 4 // Add/Modify at specific index myArray[3] = "Hello"; -// JavaScript's objects are equivalent to 'dictionaries' or 'maps' in other +// JavaScript's objects are equivalent to "dictionaries" or "maps" in other // languages: an unordered collection of key-value pairs. var myObj = {key1: "Hello", key2: "World"}; @@ -183,7 +191,7 @@ myObj.myFourthKey; // = undefined // The syntax for this section is almost identical to Java's. -// The if structure works as you'd expect. +// The `if` structure works as you'd expect. var count = 1; if (count == 3){ // evaluated if count is 3 @@ -193,18 +201,18 @@ if (count == 3){ // evaluated if it's not either 3 or 4 } -// As does while. +// As does `while`. while (true){ // An infinite loop! } // Do-while loops are like while loops, except they always run at least once. -var input +var input; do { input = getInput(); } while (!isValid(input)) -// the for loop is the same as C and Java: +// The `for` loop is the same as C and Java: // initialisation; continue condition; iteration. for (var i = 0; i < 5; i++){ // will run 5 times @@ -222,7 +230,7 @@ if (colour == "red" || colour == "blue"){ var name = otherName || "default"; -// switch statement checks for equality with === +// The `switch` statement checks for equality with `===`. // use 'break' after each case // or the cases after the correct one will be executed too. grade = 'B'; @@ -245,14 +253,14 @@ switch (grade) { /////////////////////////////////// // 4. Functions, Scope and Closures -// JavaScript functions are declared with the function keyword. +// JavaScript functions are declared with the `function` keyword. function myFunction(thing){ return thing.toUpperCase(); } 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 +// `return` keyword, otherwise you'll always return `undefined` due to // automatic semicolon insertion. Watch out for this when using Allman style. function myFunction() { @@ -291,8 +299,8 @@ 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 - // in a web browser is always 'window'. The global object may have a + // We can access the global scope by assiging 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; })(); @@ -305,7 +313,7 @@ permanent; // = 10 function sayHelloInFiveSeconds(name){ var prompt = "Hello, " + name + "!"; // Inner functions are put in the local scope by default, as if they were - // declared with 'var'. + // declared with `var`. function inner(){ alert(prompt); } @@ -313,7 +321,7 @@ function sayHelloInFiveSeconds(name){ // setTimeout is asynchronous, so the sayHelloInFiveSeconds function will // exit immediately, and setTimeout will call inner afterwards. However, // because inner is "closed over" sayHelloInFiveSeconds, inner still has - // access to the 'prompt' variable when it is finally called. + // access to the `prompt` variable when it is finally called. } sayHelloInFiveSeconds("Adam"); // will open a popup with "Hello, Adam!" in 5s @@ -329,7 +337,7 @@ var myObj = { myObj.myFunc(); // = "Hello world!" // When functions attached to an object are called, they can access the object -// they're attached to using the this keyword. +// they're attached to using the `this` keyword. myObj = { myString: "Hello world!", myFunc: function(){ @@ -345,7 +353,7 @@ var myFunc = myObj.myFunc; myFunc(); // = undefined // Inversely, a function can be assigned to the object and gain access to it -// through this, even if it wasn't attached when it was defined. +// through `this`, even if it wasn't attached when it was defined. var myOtherFunc = function(){ return this.myString.toUpperCase(); } @@ -353,37 +361,38 @@ myObj.myOtherFunc = myOtherFunc; myObj.myOtherFunc(); // = "HELLO WORLD!" // We can also specify a context for a function to execute in when we invoke it -// using 'call' or 'apply'. +// using `call` or `apply`. var anotherFunc = function(s){ return this.myString + s; } anotherFunc.call(myObj, " And Hello Moon!"); // = "Hello World! And Hello Moon!" -// The 'apply' function is nearly identical, but takes an array for an argument list. +// The `apply` function is nearly identical, but takes an array for an argument +// list. anotherFunc.apply(myObj, [" And Hello Sun!"]); // = "Hello World! And Hello Sun!" -// This is useful when working with a function that accepts a sequence of arguments -// and you want to pass an array. +// This is useful when working with a function that accepts a sequence of +// arguments and you want to pass an array. Math.min(42, 6, 27); // = 6 Math.min([42, 6, 27]); // = NaN (uh-oh!) Math.min.apply(Math, [42, 6, 27]); // = 6 -// But, 'call' and 'apply' are only temporary. When we want it to stick, we can use -// bind. +// But, `call` and `apply` are only temporary. When we want it to stick, we can +// use `bind`. var boundFunc = anotherFunc.bind(myObj); boundFunc(" And Hello Saturn!"); // = "Hello World! And Hello Saturn!" -// Bind can also be used to partially apply (curry) a function. +// `bind` can also be used to partially apply (curry) a function. var product = function(a, b){ return a * b; } var doubler = product.bind(this, 2); doubler(8); // = 16 -// When you call a function with the new keyword, a new object is created, and +// 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 // called like that are called constructors. @@ -398,7 +407,7 @@ myNewObj.myNumber; // = 5 // look at its prototype. // Some JS implementations let you access an object's prototype on the magic -// property __proto__. While this is useful for explaining prototypes it's not +// property `__proto__`. While this is useful for explaining prototypes it's not // part of the standard; we'll get to standard ways of using prototypes later. var myObj = { myString: "Hello world!" @@ -429,7 +438,7 @@ myObj.myBoolean; // = true myPrototype.meaningOfLife = 43; myObj.meaningOfLife; // = 43 -// We mentioned that __proto__ was non-standard, and there's no standard way to +// We mentioned that `__proto__` was non-standard, and there's no standard way to // change the prototype of an existing object. However, there are two ways to // create a new object with a given prototype. |