The sixth training assignment

1. Operator

Operators are used to perform program code operations . Will operate on one or more operands

2. Control statement

We wrote javascript The code is carried out from top to bottom , Many times we want the code to execute as we want , For example, selectively execute some code , This requires the use of process control statements .

There are three kinds of process statements ：

1. Process execution ： From top to bottom , From left to right

2. Choose to perform ： Branch selection

3. Loop execution ： repeat

3. choice

3.1 Single choice

if（ Conditions ）{

Statement of body ：

}

First, execute the condition

If the result is true, Then execute the statement body 1

If the result is false, Then execute the statement body 2

3.2 Multiple choice

if（ Comparison expression 1）{

Statement of body 1

}else if（ Comparison expression 2）{

Statement of body 2;

}else if（ Comparison expression 3）{

Statement of body 3;

}

3.3switch

Multiple if.....else And the value is constant , It can be used switch Replace ：

switch（ expression ）{

case value 1;

Statement of body 1;

break;

case value 2;

Statement of body 2;

break;

default：

Statement of body n+1;

[break;]

}

break Prevent penetration , without break, Then continue to execute the following code , Until I met break Or complete the execution , But sometimes penetration is used

3.4 loop

The loop structure is used to repeat an operation , Simple to understand is to repeatedly execute the same type of code , He has many forms ：

1.while: Execute before judge

2.do.....while: Judge before you execute , At least once

3.for:for( Initialization statement ; Judgment statement ; Control condition statement ）{

Loop body statement ;

}

4. Dead cycle ： Conditions are always there , For ever true, There will be a life and death cycle

5.break And continue

break： Stop this cycle

continue： Pause this cycle , Continue next time

4 Array

An array of data arranged in order , The position of each value has a number , The whole array is represented by brackets

4.1 To define an array

js There are three ways to define arrays in ：

var arr=[1,2,3];

var arr=new Array(1,2,3);

var arr=new Array(size);

4.2 Basic operation

The length of the array can be determined by length Property to get , And you can change

4.3 Array traversal

Array traversal is to access each element in the array in turn ,js Provides three ways to traverse arrays ：

1.for Loop traversal

2.for.....in

3.forEach

4. understand

4.4 The operation method provided by array

Array Object provides us with some methods , You can easily manipulate arrays

5. function

Functions as methods are pre-set blocks of code , It can be called repeatedly , According to the input parameters , Returns different values . Functions are also objects .

5.1 Function definition

There are three ways to define functions ： Function declaration statement , Function definition expression ,function Constructors

5.2 Function declaration statement

function Function name （[ parameter list ]){

}

5.3 Function definition expression

Functions defined as expressions , The name of the function is unnecessary

var Variable name =function（[ parameter list ])

5.4function Constructors

function Constructor accepts any number of arguments , But the last parameter is always regarded as a function body, also known as an expression , The previous parameters list the parameters of the new function

5.5 The parameters of the function

Sometimes, external data is required when a function is running , Different external data leads to different results , This kind of external data is called parameter , The parameters when defining are called formal parameters , The parameters when calling are called arguments

6. Function call

6.1 Commonly used call method

There is a return value that can be accepted by variables , If a function with no return value is accepted, it is unfined

2. Function call mode

3. Function call method

6.2return

Function execution may have a return value , Need to use return Statement to return the result to .return Statements are not necessary , If not, the function will not return any value

6.3 The scope of the function

Function scope ： Global and local

1. The homonymy problem of global variables and local variables

2 When you define variables in a function , If not var keyword , After use, it will automatically become a global variable