One.
<1. What is the function?
: Defined section of code, and can be used repeatedly block
<2 action functions:
Enhance code reusability will be predefined piece of code, used only when needed to trigger
Block: formation of a relatively independent scope
<3 syntax:
function function name (parameter list) {
Code block (function body) ==> block of code to be executed
return return value to return some result of the execution, the end of the function (after the program hit return, behind the return code will not be executed) can only have a return value
1. Scope function
Global function: some functions are generally written js independent function at any location in the outermost JS
Local function: the function of a function definition inside
2. The scope of variables
What is the scope?
: Life Cycle range of variables
JS in the scope of the classification:
<1. Function scope
of the variables are only accessible in the current scope
Only access to the current function, the function can not leave access
Var keyword variables defined in the body of the function is the local variables
<2. Global scope
Once defined, anywhere in the code can be accessed
Variable in the body of the function is not defined and assigned by the var keyword, it will become global variables
3. branch structure
Algorithms + data structures = programs
Any complex algorithm has the following structure:
<1, the sequence structure
<2, branch selection structure
<3, the cyclic structure
4. branch structure: meet different conditions to perform different programs
if a branch: when the conditions are met, running some statements may execute statement
if ... else ... branch: When the conditions are met, run some statement or else run the statement will perform a
Corresponding block of code when if () ... else if () .. else if () ... else satisfies a certain condition
grammar:
if (condition) {
Statement block
}
if (condition 1) {
Statement block 1
} Else if (condition 2) {
Statement block 2
} Else if (condition 3) {
Statement block 3
}...
else{
Statement block n
}
<1, under conditions such that the boolean value or expression
<2, if the conditions are not boolean then automatically converted
The following situations will be converted to false by default
if(0){}
if(0.0){}
if (in) {}
if(undefined){}
if(""){}
if(null){}
if(false){}
Apart from the above cases, the other is converted to true
if(1){}
if(2){}
if ( "The weather today is good ah!") {}
<3, the latter (condition) if {} can be omitted, but is not recommended if omitted, then if only the structure under control of the first statement if
5.switch-case structure
Action: In order to simplify determination conditions equivalent structure determination
grammar:
switch (variable / expression) {
case value 1:
Statement block 1;
break; // end of the block of statements can be omitted
case value of 2:
Statement block 2;
break;
. .. ...
default:
N-statement block;
break;
}
II. Cycle
Loop: repeat over and over again performing the same or similar code
Features:
1, cycling conditions: a predetermined number of execution cycles
2, the operation cycle: the same or displayed statement for execution
3, while the cyclic structure
while (condition) {
Loop
}
1) determining the loop condition
2) the loop condition is true, true, loop body is executed
Further determination condition, the condition is true if the loop body is executed
....
3) the loop condition is false, false, the loop operation ends
Cycle of three elements
<1, the loop variable
<2, when the execution condition is satisfied circulation loop
<3, the loop variable is the change in variation tends to condition is not satisfied, the end of the cycle tend to
4.For loop structure
grammar:
for (up to 1 represents; Expression 2; Expression 3) {
Loop
}
Expression 1: Declare variables can be omitted to declare good loop variable before the cycle begins
Expression 2: Analyzing cycling conditions may be omitted in the end of the loop to add Analyzing body of the loop will form an endless loop or
Expression 3: Update loop variable update statement can be omitted add loop variable in the loop body
Three expressions may be omitted, however; can not be omitted
Process:
1, the expression is executed declare the loop variable 1
2, determines the cycle set up condition is established is executed loop
3, executing the expression 3, updates the loop variable
2 expression execution cycle to determine whether the conditions set up set up the loop body is executed
2 expression is false result of the execution of the loop ends
Applies to: a fixed number of cycles
5.do while structure
grammar:
do{
Loop
} While (condition);
Process:
<1, first execution cycle thereof
<2, the loop condition is determined
If the loop condition holds true, the loop operation continues
If the condition is not satisfied lecture false, the loop exits
While the difference and do while
1, while: the first judgment is not executed after performing a loop may
2, do while: the first implementation, the determination is executed at least once loop