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The sixth training assignment
2022-07-07 10:57:00 【m0_ sixty-three million five hundred and fifty-two thousand nin】
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
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