Javascript权威指南

3.14  
2345.789  
.333333333333333333  
6.02e23        // 6.02 × 10  
23  
1.4738223E-32  // 1.4738223 × 10  
−32 

Math.pow(2,53)           // => 9007199254740992: 2 to the power 53  
Math.round(.6)           // => 1.0: round to the nearest integer  
Math.ceil(.6)            // => 1.0: round up to an integer  
Math.floor(.6)           // => 0.0: round down to an integer  
Math.abs(-5)             // => 5: absolute value  
Math.max(x,y,z)          // Return the largest argument  
Math.min(x,y,z)          // Return the smallest argument  
Math.random()            // Pseudo-random number x where 0 <= x < 1.0  
Math.PI                  // π: circumference of a circle / diameter  
Math.E                   // e: The base of the natural logarithm  
Math.sqrt(3)             // The square root of 3  
Math.pow(3, 1/3)         // The cube root of 3  
Math.sin(0)              // Trigonometry: also Math.cos, Math.atan, etc.  
Math.log(10)             // Natural logarithm of 10  
Math.log(100)/Math.LN10  // Base 10 logarithm of 100  
Math.log(512)/Math.LN2   // Base 2 logarithm of 512  
Math.exp(3)              // Math.E cubed  /* 何问起 hovertree.com */

Infinity                    // A read/write variable initialized to Infinity.  
Number.POSITIVE_INFINITY    // Same value, read-only.  
1/0                         // This is also the same value.  
Number.MAX_VALUE + 1        // This also evaluates to Infinity.  
Number.NEGATIVE_INFINITY    // These expressions are negative infinity.  
-Infinity  
-1/0                          
-Number.MAX_VALUE - 1  
NaN                         // A read/write variable initialized to NaN.  
Number.NaN                  // A read-only property holding the same value.  
0/0                         // Evaluates to NaN.  
Number.MIN_VALUE/2          // Underflow: evaluates to 0  
-Number.MIN_VALUE/2         // Negative zero  
-1/Infinity                 // Also negative 0  
-0  
/* 何问起 hovertree.com */

var zero = 0;         // Regular zero  
var negz = -0;        // Negative zero  
zero === negz         // => true: zero and negative zero are equal   
1/zero === 1/negz     // => false: infinity and -infinity are not equal  
// 何问起 hovertree.com

var x = .3 - .2;    // thirty cents minus 20 cents  
var y = .2 - .1;    // twenty cents minus 10 cents  
x == y              // => false: the two values are not the same!  
x == .1             // => false: .3-.2 is not equal to .1  
y == .1             // => true: .2-.1 is equal to .1 
// 何问起 hovertree.com

var then = new Date(2010, 0, 1);  // The 1st day of the 1st month of 2010  
var later = new Date(2010, 0, 1,  // Same day, at 5:10:30pm, local time  
                     17, 10, 30);  
var now = new Date();          // The current date and time  
var elapsed = now - then;      // Date subtraction: interval in milliseconds   
later.getFullYear()            // => 2010  
later.getMonth()               // => 0: zero-based months  
later.getDate()                // => 1: one-based days  
later.getDay()                 // => 5: day of week.  0 is Sunday 5 is Friday.  
later.getHours()               // => 17: 5pm, local time  
later.getUTCHours()            // hours in UTC time; depends on timezonelater.toString()   
later.toString()               // => "Fri Jan 01 2010 17:10:30 GMT-0800 (PST)"  
later.toUTCString()            // => "Sat, 02 Jan 2010 01:10:30 GMT"  
later.toLocaleDateString()     // => "01/01/2010"  
later.toLocaleTimeString()     // => "05:10:30 PM"  
later.toISOString()            // => "2010-01-02T01:10:30.000Z"; ES5 only  
// 何问起 hovertree.com

"two\nlines"   // A string representing 2 lines written on one line  
"one\          // A one-line string written on 3 lines. ECMAScript 5 only.  
 long\  
 line"  
// 何问起 hovertree.com

var s = "hello, world"        // Start with some text.  
s.charAt(0)                   // => "h": the first character.  
s.charAt(s.length-1)          // => "d": the last character.  
s.substring(1,4)              // => "ell": the 2nd, 3rd and 4th characters.  
s.slice(1,4)                  // => "ell": same thing  
s.slice(-3)                   // => "rld": last 3 characters  
s.indexOf("l")                // => 2: position of first letter l.  
s.lastIndexOf("l")            // => 10: position of last letter l.  
s.indexOf("l", 3)             // => 3: position of first "l" at or after 3  
s.split(", ")                 // => ["hello", "world"] split into substrings  
s.replace("h", "H")           // => "Hello, world": replaces all instances  
s.toUpperCase()               // => "HELLO, WORLD"  
// 何问起 hovertree.com

s = "hello, world";  
s[0]                  // => "h"  
s[s.length-1]         // => "d"  
// 何问起 hovertree.com