Reading notes----JavaScript authoritative guide (i)

0. Preface

Recently, I just finished the last section of the work, the results immediately began a new round of work, to express innocence, (O′?ェ ' O), the program Ape is really a dead tired people work.

This evening to see colleagues new unsealed JavaScript authoritative guide, the whim of thinking, if I can put the focus of the book and specific knowledge points out, then later people can not take a few detours?

Holding this idea, so began this evening's book tour, but also because of small series like to organize things this habit, only this article.

Sincerely hope to see this article of you, can feel the small make up that deep love! ~

Grammatical structure of the 1.JavaScript grammar core

1.1 Character Set 1.1.1 case sensitive

• Keywords, variables, function names, and all identifiers are all in a consistent case

• It is important to note that HTML is not size-sensitive, and some of the HTML names or property names in JavaScript must be lowercase

1.1.2 spaces, line breaks, and format controls

• Spaces between tokens in the program are ignored in JavaScript

• Our interface can be specific to the specific content of the code indentation, so to ensure that the interface
  Readability and aesthetics

1.2 Notes

Support for annotations in two formats

1. The "//" content after the end of the line can be ignored as a JavaScript comment

2. The content between "/" and "/" is also used as a comment

   • Can write across lines
   • But internal annotations cannot be nested

1.3 Direct Volume

Data values directly used in the program

1. Number 12

2. Decimal 0.12

3. string literal "Hello World"

4. Another string ' Hi '

5. Boolean value True

6. Another Boolean value of False

7. Direct amount of regular expression (used as pattern match)/javascript/gi

8. NULL NULL

9. Special Direct Volume

• Object {X:1,y:2}
• Array {* * *}

1.4 Identifiers and reserved words

The identifier is a name.

In JS, identifiers are used to name variables and functions, or to be used as a marker for jumping positions in some loop statements in JavaScript code

Naming conventions

You must start with the following:

1. Letters

2. Underline (_)

3. Dollar symbol ($)

1.5 Reserved words

Names are not arbitrarily named,

Because some of the names in the program are already occupied by the system.

For example

breakclassifelsewhile...

1.5 Optional semi-colons

, you can split the statement to enhance the readability and cleanliness of the statement,

But if there is no proper segmentation of the sentence, it will result in disastrous consequences.

想象中正确的解析方式    var y = x + f    (a + b).toString()实际的解析方式    var y = x + f(a + b).toString()

There are some old programmers who like to start with a semicolon at the beginning of every sentence,

The advantage of this is that no matter how the previous sentence is done,

The current sentence can be correctly analyzed.

2.JavaScript syntax core types, values, variables 2.1 JavaScript data types are divided into two three ways of partitioning

First Kind

原始类型    数字    字符串    布尔值    特殊的原始类型        null        undefined    代表了各自特殊类型的唯一成员对象类型    对象是属性的集合，每个属性都由 “名/值对”        值可以是原始值，如数字，字符串，也可以是对象        存在一个特殊的对象----全局对象

The second Kind

拥有方法的类型不能拥有方法的类型

Third Kind

可变类型    对象    数组不可变类型    数字    布尔值    null    undefined

2.2 Numbers

In JavaScript, integers and floating-point numbers are not distinguished, and all digits are represented by floating-point numbers.

When a number appears directly in a JavaScript program, we call it a digital direct quantity.

2.2.1 Integer Direct volume

十进制    100000十六进制    0x**    0X**八进制    不支持使用    能够通过取巧实现        0377 -> 3 * 64 + 7 * 8 + 7 = 255

2.2.2 Floating-point Direct volume

Floating-point direct quantities can contain decimal points

You can also use exponential notation to represent floating-point direct quantities

在实数后跟数字 e 或者 E 6.02e23  //6.02 * 10 ^ 23 1. 4738223E - 32    //1.4738223 * 10 ^ -32

Arithmetic operations in 2.2.3 JavaScript

Base operator

+-*/%…

Complex operators

The functions and constants defined by the properties of the Math object are implemented

Math.round(.6)     //1.0:四舍五入Math.ceil(.6)      //1.0 向上取整Math.floor(.6)     //0.0 向下取整Math.abs(-5)       //5   绝对值Math.max(x,y,z)    //返回最大值Math.min(x,y,z)    //返回最小值Math.random()      //生成一个大于0，小于 1.0 的伪随机数Math.PI            //π  3.141592673

Special cases of arithmetic operations in 2.2.4 JavaScript

Overflow (overflow)

The result of the operation exceeds the maximum number that JavaScript can represent.

• More than the positive maximum is expressed as Infinity

• The maximum of the negative is expressed as-infinity.

Underflow (underflow)

The result of the operation is infinitely close to 0 and is smaller than the minimum value that JavaScript can represent.

• Positive return 0

• Negative returns-0

• Almost the same as 0, rarely used

Divisible by zeros

Under normal condition

Return to infinity or-infinity

0 divided by 0.

Meaningless, will get NaN (not-a-number)

In addition, infinity is divided by infinity, which is the root of a negative number, and the arithmetic operator returns NaN when used with an operand that is not an arithmetic operator or that cannot be converted to a number.

These three cases do not make an error.

2.2.5 Binary Floating-point and rounding errors

The numbers in JavaScript are accurate enough, but occasionally they can cause some problems.

var.3.2;      /*三十美分减去二十美分*/var.2.1;  /*二十美分减去十美分*//*false*/x==.1                 /*false*/y==.1                 /*true*/

Cause: 0.3-0.2 = 0.09999999999999999998 under real-world operating conditions

2.2.6 Date and time

The Date () constructor is included in JavaScript

Used to create an object that represents a date and time

For example

varthen =New Date( .,0,1);//January 1, 2011varthen =New Date( .,0,1， -,Ten, -);//January 1, 2011 local time 5:10:30pmvarnow =New Date();//Current date and timevarelapsed = Now-then;//Date subtraction, the number of milliseconds to calculate the time intervalLater.getfullyear ()//2011Later.getmonth ()//month starting from 0 countingLater.getdate ()//number of days to count starting from 1Later.getday ()//Get Day of the week, 0 means Sunday, 5 means week 1Later.gethours ()//local timeLater.getutchours ()//Use UTC to indicate hours, based on time zone

Today's reading notes are first written here, because it has been July 11, 2016 22:36:18, I also need to go home to sleep, the next article update time is not sure, anyway, there must be time to update.

Finally wish each small partner work smoothly! ~

Sapo roll to seek praise! ~ The clatter! ~

Reading notes----JavaScript authoritative guide (i)