javascript中的数据类型

var result = typeof(null);
document.write("typeof null =" + result);	// object
document.write("</br>");

上面result的结果是object

var sum = "1" + 2 + 3;
document.write("‘1‘ + 2 + 3 = " + sum);		// 123
document.write("</br>");
var sum1 = "64" - 4;
document.write("‘64‘ - 4 = " + sum1);		// 60
document.write("</br>");
var sum2 = NaN * 4;
document.write("NaN * 4 = " + sum2);		// NaN
var result1 = void(0);
document.write("</br>");
document.write("void(0) = " + result1);		// undefined
var result2 = null * 45;
document.write("</br>");
document.write("null * 45 = " + result2);	// 0
var result3 = 13 | 5;						
document.write("</br>");
document.write("13 | 5 = " + result3);		// 13
var result4 = 13 & 5;						
document.write("</br>");
document.write("13 & 5 = " + result4);		// 5
var result5 = 13 >> 2;						
document.write("</br>");
document.write("13 >> 2 = " + result5);		// 3
var result6 = -13 >> 2;						
document.write("</br>");
document.write("-13 >> 2 = " + result6);	// -4
var result7 = 13 << 2;						
document.write("</br>");
document.write("13 << 2 = " + result7);		// 52
var result8 = -13 << 2;						
document.write("</br>");
document.write("-13 << 2 = " + result8);	// -52
var str = "abdc.#dfe.%^%$";
str = str.toUpperCase();
document.write("</br>");
document.write("str.toUpperCase = " + str);	// ABDC.#DFE.%^%$
var num1 = parseInt("28");
document.write("</br>");
document.write("parseInt(‘28‘) = " + num1);	// 28
var num2 = parseInt("028");
document.write("</br>");
document.write("parseInt(‘028‘) = " + num2);	// 2	(注意：8进制的数不能有8和9)
var num3 = 11;
var str1 = num3.toString(2);
document.write("</br>");
document.write("十进制数11变为2进制 = " + str1);  // 01111011

var str4 = "hello world!";
str4.replace(/world/,"my friend");	       // hello world
document.write("</br>");
document.write("str4 = " + str4);