JavaScript function definition, parameter call

I. JavaScript functions
Function: a function is an encapsulation, event driven, or reusable block of code that executes when it is called.
Define function:
Function function name (){
Function body;
}
The number will not be automatically executed. It needs to be called before it can be executed
Function name ();
Function naming rules:
Consistent with variable naming rules
1) start with letters,,, 2) can contain numbers, letters,,, 2) can contain numbers, letters
open

The first 2) can contain numbers, letters_
3) case sensitive
4) cannot use keywords and reserved words
Hump nomenclature: if the name consists of more than one word, start with the second word and capitalize the first letter
Distinguish variable name and function name
Unwritten rules:
Function name verb
Variable NOUN
The order in which functions are defined is independent of the order in which they are called

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script type="text/javascript">
//Output 5 lines of hello world on the page
//Defined function
function printHello(){
for(var i=0;i<5;i++){
document.write('hello world<br>');
}
}
printHello(); function call
</script>
</body>
</html>

2. Function parameter call;
Parameters: parameters in function definition
Arguments: arguments for function consumption
Theoretically, a function can have an infinite number of parameters separated by commas
Unlimited function parameter types

Case 1
/Print graphics
*
***
*****
*******
*********
...
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script type="text/javascript">
function show(row){
for(i=1;i<=row;i++){
for(j=1;j<=2*i-1;j++){
document.write('*');
}document.write('<br>');
} 
}
show(5);
</script>
</body>
</html>

Case 2
//Calculate the area of a rectangle
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script type="text/javascript">
function calRet(w,h){
var w;
var h;
var area=w*h;
console.log(area);
}
calRet(20,10);
</script>
</body>
</html>

Case 3: multiple function parameters
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script type="text/javascript">
function person(name,age,gender){
var man='Sir';

if (!gender) {
man='Ma'am';
}document.write('Welcome'+name+man+'Visit to school,Age:'+age+'<br>');
}
person('Cockroach',60,true);
person('Cockroach',60,false);
</script>
</body>
</html>

Case 4: time call
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script type="text/javascript">
var o=document.getElementById('box');
function showTime(){
//Get year, month, day
var date = new Date;
var year=date.getFullYear();
var month=date.getMonth()+1;
var day=date.getDate();
//Get hour, minute, second
var hour=date.getHours();
var minute=date.getMinutes();
var second=date.getSeconds();

hour=add(hour);
minute=add(minute);
second=add(second);

time=year+'/'+month+'/'+day+' '+hour+':'+minute+':'+second;
o.innerHTML=time;
}
function add(num){
if (num<10) {
num='0'+num;
}
return num;
}
showTime();
setInterval(showTime,1000);
</script>
</body>
</html>

Keywords: Java Javascript

Added by Kookedoh on Mon, 02 Dec 2019 06:55:12 +0200

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JavaScript function definition, parameter call

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