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String.prototype usage examples in JavaScript_javascript skills

May 16, 2016 pm 03:58 PM
javascript

本文实例讲述了JavaScript中String.prototype用法。分享给大家供大家参考。具体如下:

// 返回字符的长度,一个中文算2个
String.prototype.ChineseLength=function()
{ 
  return this.replace(/[^\x00-\xff]/g,"**").length;
}
// 判断字符串是否以指定的字符串结束
String.prototype.EndsWith = function(str) 
{
  return this.substr(this.length - str.length) == str;
}
// 去掉字符左端的的空白字符
String.prototype.LeftTrim = function()
{
  return this.replace(/(^[\\s]*)/g, "");
}
// 去掉字符右端的空白字符
String.prototype.RightTrim = function()
{
  return this.replace(/([\\s]*$)/g, "");
}
// 判断字符串是否以指定的字符串开始
String.prototype.StartsWith = function(str) 
{
  return this.substr(0, str.length) == str;
}
// 去掉字符两端的空白字符
String.prototype.Trim = function()
{
  return this.replace(/(^\s*)|(\s*$)/g, "");
}
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这就是我们经常看到的为内部对象, 如 String, Math 等再添加其它属性和方法的技巧. 对于任何的内部对象和自定义对象, 你都也可以通过 prototype 来重载其下的属性和方法. 那么在调用执行时, 它将调用你所定义的方法和属性. 下面是示例:

// 为内部 String 对象添加方法
String.prototype.myMethod = function(){
 return "my define method";
}
// 为内部 String 对象重载方法
String.prototype.toString = function(){
 return "my define toString method";
}
var myObj = new String("foo");
alert(myObj.myMethod());
alert(myObj);
alert("foo".toString());

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另外需要注意的是, 所有 JavaScript 内部对的 prototype 属性都是只读的. 你可以像上面那样为内部对象的原型添加或重载属性和方法,但不能更改该内部对象的 prototype 原型. 然而, 自定义对象可以被赋给新的原型. 也就是说, 像下面这样做是没有意思的.

function Employee() {
 this.dept = "HR";
 this.manager = "John Johnson";
}
String.prototype = new Employee;
var myString = new String("foo");

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上面的程序在运行之后不会报错, 但显然, 如果你调用 myString.dept 将会得到一个非定义的值.

另外, 一个经常使用的是 prototype 下的 isPrototypeOf() 方法, 它主要用来判断指定对象是否存在于另一个对象的原型链中. 语法如下:

object1.prototype.isPrototypeOf(0bject2);

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上面的格式是用来判断 Object2 是否出现 Object1 的原型链中. 示例如下:

function Person() {
 this.name = "Rob Roberson";
 this.age = 31;
}
function Employee() {
 this.dept = "HR";
 this.manager = "John Johnson";
}
Employee.prototype = new Person();
var Ken = new Employee();

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当执行 Employee.prototype.isPrototypeOf(Ken), Person.prototype.isPrototypeOf(Ken) 和 Object.prototype.isPrototypeOf(Ken) 时, 结果都会返回 true.

希望本文所述对大家的javascript程序设计有所帮助。

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