Javascript basic finishing (ES5)

Javascript主要分为ECMAScript + DOM + BOD

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Preface

输出语句

• console.log() is actually the method under window.console.log() window object
• alert() is actually the method under window.alert() window object

REPL环境

1. Read
2. Eval execution
3. Print
4. Loop

前端三层

1. Structural layer
2. Style layer
3. Behavioral layer

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*variable

定义变量

The var keyword defines a variable or defines multiple variables at the same time, separated by ','

When
the variable defined by var a is not assigned an initial value, the default value is undefined

have b = 13
关键字 变量 赋值运算符 值

var c = 13, d = 15
define multiple variables at the same time

变量的提升

• Only promote the variable name, not the value
• Before executing all the code, JS has a pre-analysis stage, which will pre-read the definition of all variables. This is the reason why variables can be improved.

变量的使用

console.log(a)
变量使用时不能加引号

改变变量的值

When changing the value of a variable, there is no need to write the keyword var, just assign the value by the assignment operator

变量的命名规则

1. Only in 字母, 下划线, 数字, $symbols,Cannot start with a number
2. No keywords or reserved words
3. Case sensitive, a and A are different

Variable naming rules also apply to identifier naming rules
Identifiers: functions, class names, object attributes, etc.

Excellent variable nomenclature
1, 驼峰命名法mathTestScore
2, c风格math_test_score

变量常见错误

• Without var definition, although no error will be reported, the variable will become a global variable, which will cause scope problems
• Use a variable that is neither defined nor assigned, an error will be reported (reference error)

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*type of data

数据类型简介和检测

Two data types in JS: basic type with Reference type

typeofOperator detects the type of value or variable

typeof 5    //number
typeof null    //object
type of NaN     //number
typeof undefined   //undefined

Values ​​of the null data type and undefined data type, only the respective null and undefined

基本数据类型

1. String type

   Strings are spliced ​​with + sign

   The length attribute of the string can indicate the length of the string

   var a='123'
   console.log(a.length)    //输出4
   

   String common methods

2. Number type

   0 in decimals can be omitted

   Scientific notation: 3e8 is the same as 3 times 10 to the 8th power
   较大数或者较小数可以写成科学计数法 ，如3e8，或3e-8

   NaN
   special number type value, not a number

3. Boolean type

4. null type

5. undefined type

复杂数据类型简介（引用数据类型）

1. Array
2. Object

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*Expressions and operators

JS基本表达式

Arithmetic expression

Arithmetic expression

JS运算符

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*JS flow control statement

条件语句

循环语句

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*algorithm

什么是算法

累加器和累乘器

穷举法

综合算法

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*Array

数组简介及定义/数组类型检测

数组常用方法

数组算法

_{Traverse related algorithms}

_{Array deduplication and random samples}

_{Bubble Sort}

_{Two-dimensional array}

数组的深浅克隆

_{Memory change of basic type value passing by value (stack storage)}

_{Memory change of reference type value passing by value (heap storage)}

_{Shallow clone}

_{Deep clone}

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*function

函数基本使用

_{What is a function}

_{Function definition and call}

_{Function parameters and return values}

函数算法题

递归

作用域和闭包

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