js～示例Global對象

測試一下全局對象的部分屬性和方法

 

*Gobal內容

---屬性

NaN, 表示非數字

Infinity, 表示無限大數字

debugger, 還不知道如何使用?

undefined , 表示一個實例沒有定義任何值,是一個特殊的基本類型

---方法

eval, 執行一段string格式的javascript腳本, 將執行結果放在eval位置上.(可能需要一篇專門的文章討論其執行作用域問題).

parseInt, (詳見,http://www.w3schools.com/jsref/jsref_parseint.asp)

parseFloat, (詳見, http://www.w3school.com.cn/js/jsref_parseFloat.asp)

escape,unescape,(ECMA不推薦,見http://www.w3school.com.cn/js/jsref_escape.asp)

isNaN, if 非數字 return true, 否則 false

isFinite, if InFinity return false, 否則 true

decodeURI,encodeURI (字母數字和屬於URI特殊字符的保持原樣, 其他的字符編碼,如空格替換為'%20')

decodeURIComponent,encodeURIComponent (編碼所有非字母數字的字符,使用時需注意,否則url非法)

 

*示例

---源碼 （在Node中測試）

//attribute
console.log("//test NaN");
if(NaN)
    console.log("NaN is true");
else
    console.log("NaN is false");
console.log("NaN's value: " + NaN);
console.log("NaN's type: " + NaN);
console.log("\n");

console.log("//test Infinity");
if(Infinity)
    console.log("Infinity is true");
else
    console.log("Infinity is false");
console.log("Infinity's value: " + Infinity);
console.log("Infinity's type: " + Infinity);
console.log("\n");

console.log("//test undefined");
if(undefined)
    console.log("undefined is true");
else
    console.log("undefined is false");
console.log("undefined's value: " + undefined);
console.log("undefined's type: " + undefined);
console.log("\n");

/**
console.log("//test debugger");
if(debugger)
    console.log("debugger is true");
else
    console.log("debugger is false");
console.log("debugger's value: " + debugger);
console.log("debugger's type: " + debugger);
console.log("\n");
*/

//function
console.log("//test escape/unescape");
var str =  escape("dai zhong");
console.log("escape(string): " + str);
console.log("unescape(string): " + unescape(str));
console.log("\n");

console.log("//test encodeURI/decodeURI");
var url = "http://www.cnblogs.com/bronte 戴忠的博客";
url = encodeURI(url);
console.log("encodeURI: " + url);
console.log("decodeURI: " + decodeURI(url));
console.log("\n");

console.log("//test encodeURIComponent/decodeURIComponent");
var url = "http://www.cnblogs.com/bronte 戴忠的博客";
url = encodeURIComponent(url);
console.log("encodeURIComponent: " + url);
console.log("decodeURIComponent: " + decodeURIComponent(url));
console.log("\n");

console.log("//test eval");
var str = "eval";
eval("console.log(str)"); // eval
console.log("\n");

console.log("//test isFinite");
if(isFinite(Infinity))
    console.log("isFinite(Infinity) is true");
else
    console.log("isFinite(Infinity) is false");
if(isFinite(11))
    console.log("isFinite(11) is true");
else
    console.log("isFinite(11) is false");
console.log("\n");

 

---結果

//test NaN
NaN is false
NaN's value: NaN
NaN's type: NaN


//test Infinity
Infinity is true
Infinity's value: Infinity
Infinity's type: Infinity


//test undefined
undefined is false
undefined's value: undefined
undefined's type: undefined


//test escape/unescape
escape(string): dai%20zhong
unescape(string): dai zhong


//test encodeURI/decodeURI
encodeURI: http://www.cnblogs.com/bronte%20%E6%88%B4%E5%BF%A0%E7%9A%84%E5%8D%9A%E5%AE%A2
decodeURI: http://www.cnblogs.com/bronte 戴忠的博客


//test encodeURIComponent/decodeURIComponent
encodeURIComponent: http%3A%2F%2Fwww.cnblogs.com%2Fbronte%20%E6%88%B4%E5%BF%A0%E7%9A%84%E5%8D%9A%E5%AE%A2
decodeURIComponent: http://www.cnblogs.com/bronte 戴忠的博客


//test eval
eval


//test isFinite
isFinite(Infinity) is false
isFinite(11) is true

  

*總結

---全局對象是一個特殊的內置對象, 由解析器在初始化時創建, 具體如何實現有具體環境決定, 如瀏覽器中的window對象就是全局對象;

---全局對象表示的是所有對象的根對象, 比如js的語法之一,name = "dzh",這個name沒有用var聲明, 那么name被添加到了全局對象的屬性上;

---所以它提供了最為常用的功能和屬性定義.

 

*參考

http://www.w3school.com.cn/js/jsref_obj_global.asp