JavaScript authoritative Guide Learning Note 2

JavaScript language Core (2~12 chapter)

Chapter III: Types, values, variables

1. Numbers:

• Overflow (Infinity,-infinity), underflow (+0,-0)
• Non-numeric value: It is not equal to any value, including itself. if (x! =X) return nan;== "IsNaN () judgment is not NAN or string etc.
• The accuracy of JavaScript should be noted, IE (0.3-0.2)! = (0.2-0.1)
• Date () constructor: The month is counted starting from 0, the number of days starts at 1, and Sunday is 0;

2. Text:

• Escape character (keep in mind a few special values behind the slash: N,\,r,v,t,f,b,o, ",")
• Method of String (Length,charat,substring,slice,indexof,split,replace,touppercase)
• Regular Expression!!!!

3. Boolean value: false Example (Undefined,null,0,-0,nan, "")

4.null and Undefined:null are non-objects, undefined are undefined

5. Global objects:

6. Packaging objects:

7. Immutable Original values:

 1  function   Equalarrays (A, b) { 2  if  (a.length!=b.length) return  false  ;  3   var  i=0;i<a.length;i++)  4  
   
    if  (A[i]!==b[i]) 
    false  Span style= "color: #000000;" >; 
    5  
    return  
    true  
     6 } 
   

determine if an array is equal

8. Type conversion: conversion and equality, mainly converted to a number for comparison and other operations, if no meaning is converted to Nan; Display type conversions are similar to numbers ("3"), such as C and Viet Nam, and the ToString () method will throw exceptions except for null and undefined, and others will not.

9. Variable declaration:

10. Variable Scope:

1 functionTest (o) {2     varI=0;3     if(typeofo== "Object"){4         varJ=0;5          for(vark=0;k<10;k++){6Console.log (k);//0~97         }8Console.log (k);//Ten9     }TenConsole.log (j);//undefined One}

Scope

JavaScript authoritative Guide Learning Note 2