[Web Test] JavaScript function definition and call

Function

    • 1. Definition and calling of functions
    • 2. Anonymous functions

1. Definition and calling of functions

1. Function: also known as “method”, solves the problem: realizes the encapsulation of code blocks corresponding to different functions

?Example: Function/method—–>Encapsulated code block—–>Realize a certain function

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<script language="javascript">
//Fun01 with no parameters and no return value
function fun01(){
alert("This is a button!");
}
fun01();
</script>
</body>
</html>

2.Declaration/Create function

function function name (Parameter name 1, Parameter name 2…){

? Function body;—->The code block corresponding to the function to be implemented by the function

return return value;

}

Remarks: ① The parameters within parentheses are writable;

? ②The return statement can be written. If the function needs to have a return value, associate it;

? ③The parameters set when declaring the function are called == “formal parameters” , referred to as “formal parameters”==;

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<script language="javascript">
//Function fun02 with parameters and no return value
function fun02(x,y,z){
alert(x-y-z);
}
fun02(100,40,35);
</script>
</body>
</html>

3.Function call: Run/execute the created function

Format: function name(); or function name(actual parameters);

Remark:

? Actual parameters: Actual parameters, which refers to the assignment operation performed when calling a function with formal parameters;

? Actual parameter is the value assigned to the formal parameter: The actual parameter is passed to the formal parameter

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<script language="javascript">
//Function fun03 with no parameters and return value
function fun03(){
return(Math.random()*100);
}
var f=fun03();
alert(f)
</script>
</body>
</html>

4.return statement:

There is no output function, it can only return data. If you want to display the returned result value, you have to use an output statement;

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<script language="javascript">
//Function fun04 with parameters and return value
function fun04(i,j,k){
alert("The multiplication of three numbers is:");
return(i*j*k);
}
//var ijk=fun04(Math.random(),Math.random(),Math.random());
//alert(ijk);
var ijk=fun04(fun03(),fun03(),fun03());
alert(ijk);
</script>
</body>
</html>

2. Anonymous functions

1.Overview: Functions have no names and are used in combination with variables

2.Format:

var variable name=function(Parameter name){

? Function body;

? return return value;

}

3. Call: variable name(); variable name(value);

Example:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Anonymous function</title>
\t\t
<script language="JavaScript">
\t\t\t
//Declare an anonymous function: implement the remainder operation of two numbers
//Anonymous function with parameters and return value
var fun01=function(x,y){//x=10 y=24
\t\t\t\t
//Return the remainder result
return x%y; //63%9=0
}
\t\t\t//transfer
alert(fun01(10,24));
\t\t\t
alert(fun01(11,10));
\t\t\t
//Declare an anonymous function with no parameters and no return value
var fun02=function(){
//Output
alert("I am an anonymous function with no parameters and no return value");
}
\t\t\t//transfer
fun02();
</script>
</head>
<body>
</body>
</html>

4. Global functions: functions that can be used directly;

1> eval(): Identify and execute the JS code contained in the string;

2>Chinese encoding: encodeURI()

Example:

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Encoding</title>
</head>
<body>
<script language="javascript">
//Me and my motherland
var name=prompt("Please enter...");
var bbb=encodeURI(name);
if(bbb=="My motherland and I"){
alert("Verified correctly!");
}else{
alert("Big idiot!");
}
</script>
</body>
</html>

3> Chinese decoding: decodeURI()

Example:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>js</title>
\t\t
<script language="JavaScript">
//③Chinese decoding: decodeURI()
var i="A loving family";
//Decode the value of i
var jm=decodeURI(i);
//Output A family that loves each other
console.log(jm);
\t\t\t
</script>
\t\t
</head>
<body>
</body>
</html>

JavaScript Chinese decoding

4> isNaN(): Determine whether it is a number, is a number returns false, is not a number returns true: see Literal value

Example:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>js</title>
\t\t
<script language="JavaScript">
//isNaN(): Determine whether it is a number. If it is a number, it returns false. If it is not a number, it returns true: look at the literal value.
var x="testing";
var y=26;
var z="69";
console.log(isNaN(x)); //true
console.log(isNaN(y)); //false
console.log(isNaN(z)); //false
</script>
\t\t
</head>
<body>
</body>
</html>

isNaN function

5> parselnt(): Convert the numbers in the string to the original data type;

Example:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>js</title>
\t\t
<script language="JavaScript">
\t\t\t
//parseInt(): Convert the numbers in the string to the original data type
var s="123";
alert(s + 1); //1231
alert(parseInt(s) + 1); //124
</script>
</head>
<body>
</body>
</html>

parselnt function