function
Function function
Function: put the code of the same function together
Function: encapsulation + reusability
Function classification:
1. System function ()
2. User defined function
Function: it is a tool that can be reused. Some functions have parameters and some do not. Such as math random(),alert(666)
Syntax of function:
Function function name (parameter){
How is the function realized
}
Note: function name (parameter) - the function must be called
The description of the function includes:
1. Function: sum two numbers
2. Parameter Description: (declare the type of parameter)
The first parameter is a number
The second parameter is also a number
Summation by function
//instructions
//Function function: find the sum of two numbers
//Arguments to function:
//The first parameter is a number
//The second number is also a number
//Define a function function function name (parameter)
function sum(m,n){
//Print the sum of m,n
document.write(m+n);
}
//Call function
sum(2,3);
Encapsulation of functions
Steps of function encapsulation:
1. Ordinary to achieve this function
2. Install a shell function
3. Choose a name
4. Consider whether parameters are required - parameters are optional
5. Be sure to call the function
6. Attach instructions
Training: printing triangles using function encapsulation
function star(m){
//Outer loop print * lines
for(var i = 1 ; i <= m ; i++){
//Inner loop print one line * number
for(var j = 1 ; j <= i ; j++){
//Print*
document.write('*')
}
//Line feed
document.write('<br>')
}
}
//Call the function to print the triangle
star(5) ;
Formal and actual parameters of function:
Where the function is declared: formal parameters
Where the function is called: Arguments
//Function: print multiplication table
//Arguments to function:
//The first parameter is the number number -- print a multiplication table
// m and n are called formal parameters --- formal parameters
function multi_99(m , n) {
for(var i = 1 ; i <= m ; i++){
for(var j = 1 ; j <= i ; j++){
if(n === '*'){
document.write(j + '*' + i + '=' + i * j + ' ');
}
else if(n === '+'){
document.write(j + '+' + i + '=' + (i + j) + ' ' );
}
}
document.write('<br>');
}
}
//5 6 * + called actual parameter -- actual parameter
multi_99(5 , '*');
multi_99(6 , '+ ');
Training: use the encapsulation of function to output prime numbers within 1-100 and wrap lines
//Function function: output prime numbers within 100 and wrap lines
//The first parameter is number -- number. Enter a prime number within 0-A few
//The second parameter is number -- number. Enter several numbers and change one line
function isZhi(n , m){
//First traverse the number of 1-100
var count = 0 ;
for(var i = 2 ; i <= n ; i++){
//Find a prime number that satisfies the condition, assuming it is a prime number
var flag = true;
//Find evidence of no - not as long as it can be divided by any number
for(var j = 2 ; j < i ; j++){
//As long as it can be divided by other numbers
if(i % j === 0){
//The explanation is not a prime number, that is, the hypothesis is overturned
flag = false ;
//The results have come out, there is no need to continue to look for evidence
break ;
}
}
//Finally, judge whether it is a prime number according to the value of flag
//flag ? document.write(i) : '';
if(flag){
document.write(i + ' ');
count++;
//Wrap every m
if(count === m){
document.write('<br>');
count = 0 ;
}
}
}
}
isZhi(100 , 5);
Return value of function
Return value of function - the result of the final execution of the function
The return value of the function is also optional
When a variable is defined inside a function, it cannot be used outside. An error will be reported because the internal variable of the function cannot be accessed.
function sum(a , b){
//Just print the result on the console
// console.log(a+b);
var result = a + b ;
//result is defined inside the function and cannot be used outside
// console.log(result);
return result
}
var n = sum(2 , 3) ;
document.write(n);
// document.write(result); / / an error is reported because the internal variable of the function cannot be accessed
var n = Math.random();
console.log(n); //Function will get a result
var res = alert(666);
console.log(res); //No results show undefined
Training: encapsulating random numbers
function rand(max , min){
// var n = Math.round(Math.random()*(max - min) + min) ;
// return n ;
return Math.round(Math.random()*(max - min) + min) ;
//At this time, you need to print outside the function. You must return, otherwise undefined will be displayed
}
var m = rand(200,100);
document.write(m);
Training: judge whether a number is a prime number by using the encapsulation of the function, and output a prime number within 1-100
Insert the code slice here //Judge whether a genus is a prime number
function isZhi(x){
var flag = true ;
for(var i = 2 ; i < x ; i++){
if(x % i === 0){
flag = false ;
break;
}
}
// if (flag){
// return true ;
// }
// else{
// return false ;
// }
return flag ;
}
var r1 = isZhi(12) ; //false
var r2 = isZhi(17) ; //true
document.write(r1 , r2) ;
//All prime numbers within 100
// for(var i = 2 ; i<= 100 ; i++){
// var r4 = isZhi(i);
// if(r4){
// document.write(i);
// }
// }
for(var i = 2 ; i <= 100 ; i++) {
var r4 = isZhi(i) ;
if(r4) {
document.write(i)
}
}
Training: call the function. 1. Generate a random number within the specified range and judge whether the number is a prime number; 2. Randomly generate two numbers and call the function to sum, difference, multiply and divide.
html code:
<body>
Generate 100-200 The random numbers between are:<input type="text" id="inp1">
<br>
Judge whether he is a prime number:<input type="text" id="inp2">
<script src="../js/tools_02.js"></script>
<script>
//Generate a random number of 100-200 to judge whether it is a prime number
//Call the function that generates the random number
var n = rand(100,200)
//Determine whether the generated random number is a prime number
var res = isZhi(n) ;
console.log(n , res)
//Get object
var oInp1 = get('inp1');
var oInp2 = get('inp2');
oInp1.value = n;
if(res){
oInp2.value = 'Is a prime number'
}
else{
oInp2.value = 'Not a prime number'
}
//The operation of calculating two numbers
var n1 = rand(0 , 100) ;
var n2 = rand(0 , 100) ;
var res2 = jiSuanQi(n1 , n2 , '-') ;
document.write(n1 + '-' + n2 + '=' + res2);
</script>
</body>
js code:
//Function: generate random integers in a certain range
//Parameters:
// Min number range min
// Max number range Max
//Return value:
// number
function rand(min , max){
return Math.round(Math.random()*(max - min) + min)
}
//Judge whether a genus is a prime number
//Parameters:
// number
//Return value:
// boolean
function isZhi(x){
for(var i = 2 ; i < x ; i++){
if(x % i === 0){
return false;
}
}
return true;
}
//Get object
function get(id){
return document.getElementById(id)
}
//Calculator
function jiSuanQi(a , b , f){
switch(f){
case '+' : return a + b ;
case '-' : return a - b ;
case '*' : return a * b ;
case '/' : return a / b ;
}
}
Function notes:
alert(666) calls the function directly and passes a parameter
var n = Math.random() calls the function and accepts the result with a variable
Return value: 1. Result of function execution; 2. End the whole loop in advance
return: end the function ahead of time