Javascript学习笔记（一）

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本文介绍了JavaScript中的一些核心概念，包括原始数据类型的包装对象、值传递与引用传递的区别、运算符的使用方法等，并详细讲解了数组的各种常用方法如join、reverse、sort、concat、slice和splice的功能及用法。

1.原生数据类型包装对象（Primitive Datatype Wrapper Objects）: note that any number, string, or boolean value can be converted to its corresponding wrapper object with the Object( ) function:
var number_wrapper = Object(3);

2.number,boolean,string按值传递 object按引用传递

3. == 和 === 的不同点：===在两边的类型不一致时直接返回false,不考虑类型转换

4.in operation:The in operator expects a left-side operand that is or can be converted to a string. It expects a right-side operand that is an object (or array). It evaluates to TRue if the left-side value is the name of a property of the right-side object.

5.instanceof operation:表示是否是某一个类的实例。

6.“delete” operator:delete is a unary operator that attempts to delete the object property, array element, or variable specified as its operand

7.for/in operator:
statement. This statement is a somewhat different kind of loop with the following syntax:
for (variable in object)
statement

8.Array methods:

join():The Array.join() method converts all the elements of an array to strings and concatenates them. You can specify an optional string that separates the elements in the resulting string. If no separator string is specified, a comma is used.

reverse():反转，调换数组排序

sort(): 排序方法

var a = [33, 4, 1111, 222];
    a.sort();                 // Alphabetical order: 1111, 222, 33, 4
    a.sort(function(a,b) {    // Numerical order: 4, 33, 222, 1111
           return a-b;    // Returns < 0, 0, or > 0, depending on order
       });

concat:拼接

var a = [1,2,3];
a.concat(4, 5)          // Returns [1,2,3,4,5]
a.concat([4,5]);        // Returns [1,2,3,4,5]
a.concat([4,5],[6,7])   // Returns [1,2,3,4,5,6,7]
a.concat(4, [5,[6,7]]) // Returns [1,2,3,4,5,[6,7]]

slice():切割

var a = [1,2,3,4,5];
a.slice(0,3);    // Returns [1,2,3]
a.slice(3);      // Returns [4,5]
a.slice(1,-1);   // Returns [2,3,4]
a.slice(-3,-2); // Returns [3]

splice(): 截取

var a = [1,2,3,4,5,6,7,8];
a.splice(4); // Returns [5,6,7,8]; a is [1,2,3,4]
a.splice(1,2); // Returns [2,3]; a is [1,4]
a.splice(1,1); // Returns [4]; a is [1]
a.splice(0); //return [1,2,3,4,5,6,7,8];a is [];