JavaScript学习更新-01

http://learn.jquery.com/javascript-101/conditional-code/

更新的知识点如下：

1. 知道有这个符号  ===

var foo = 1;
var bar = 0;
var baz = "1";
var bim = 2;
foo == bar; // false
foo != bar; // true
foo == baz; // true; but note that the types are different
alert("===11111"+(foo ===baz)); // false
foo !== baz; // true
foo === parseInt( baz ); // true
foo > bim; // false
bim > baz; // true
foo <= baz; // true

2.switch的另外一种写法

var stuffToDo = {
    "bar": function() {
        alert( "the value was bar -- yay!" );
    },
    "baz": function() {
        alert( "boo baz :(" );
    },
    "default": function() {
        alert( "everything else is just ok" );
    }
};

var foo = "baz";

if ( stuffToDo[ foo ] ) {
stuffToDo[ foo ]();
} else {
stuffToDo[ "default" ]();
}

3. JS编码规范

Google JavaScript Style Guide

4.Array的排序

 

function descending( a, b ) {
  alert("****"+b+"****a****"+a+"((((("+(b-a));
    return b - a;
    }

var myArray = [ 3, 4, 6, 8 ];

alert(myArray);


  alert(myArray.sort( descending ));

这个不知道为什么最后会打印 【8,6,4,3】

5. Array的 forEach函数

function printElement( elem ) {
        alert( elem );
        }
        
        
        function printElementAndIndex( elem, index ) {
        alert( "Index " + index + ": " + elem );
        }
        
        
        function negateElement( elem, index, array ) {
        array[ index ] = -elem;
        }
        
        
        myArray = [ 1, 2, 3, 4, 5 ];
        // Prints all elements to the console
        myArray.forEach( printElement );
        // Prints "Index 0: 1", "Index 1: 2", "Index 2: 3", ...
        myArray.forEach( printElementAndIndex );
        // myArray is now [ -1, -2, -3, -4, -5 ]
        myArray.forEach( negateElement );
        alert(myArray);

6.Objects

As it turns out, nearly everything in JavaScript is an object – arrays, functions, numbers, even strings – and they all have properties and methods.

var myObject = {
sayHello: function() {
console.log( "hello" );
},
myName: "Rebecca"
};
myObject.sayHello(); // "hello"
console.log( myObject.myName ); // "Rebecca"

7. function

// Function declaration.
function foo() {
// Do something.
}

// Named function expression.
var foo = function() {
// Do something.
};

（2）函数作为参数的2种方式：

// Passing an anonymous function as an argument.
var myFn = function( fn ) {
var result = fn();
console.log( result );
};
// Logs "hello world"
myFn( function() {
return "hello world";
});

// Passing a named function as an argument
var myFn = function( fn ) {
var result = fn();
console.log( result );
};
var myOtherFn = function() {
return "hello world";
};
myFn( myOtherFn ); // "hello world"

8.Testing Type

// Testing the type of various variables.
var myFunction = function() {
console.log( "hello" );
};
var myObject = {
foo: "bar"
};
var myArray = [ "a", "b", "c" ];
var myString = "hello";
var myNumber = 3;
typeof myFunction; // "function"
typeof myObject; // "object"
typeof myArray; // "object" -- Careful!
typeof myString; // "string"
typeof myNumber; // "number"
typeof null; // "object" -- Careful!
if ( myArray.push && myArray.slice && myArray.join ) {
// probably an array (this is called "duck typing")
}
if ( Object.prototype.toString.call( myArray ) === "[object Array]" ) {
// Definitely an array!
// This is widely considered as the most robust way
// to determine if a specific value is an Array.
}

8.The “this” Keyword

9.Scope &&Closures