Javascript learning notes (7) Functions

1. function internal attribute arguments
Arguments is used to save the function parameters. arguments. callee points to a function with an arguments object.

1 // factorial
2 function factorial (num ){
3 if (num <= 1 ){
4 return 1;
5} else {
6 return num * arguments. callee (num-1); // use agreements. callee instead
7}
8}
9
10 var trueFactorial = factorial;
11 factorial = function {
12 return 0;
13}
14 alert (trueFactorial (5); // 20
15 alert (factorial (5); // 0
2. Function Attributes and Methods
Length attribute, indicating the number of function parameters

3. apply () and call () Methods
The apply () and call () methods are used to pass parameters or expand the function scope.

1 // PASS Parameters
2 function sum (num1, num2 ){
3 return num1 + num2;
4}
5 function callSum (num1, num2 ){
6 return sum. call (this, num1, num2); // The first parameter this, which is listed later
7}
8 alert (callSum (10, 10); // 20
9
10 function calSum1 (num1, num2 ){
11 return sum. apply (this, arguments); // The first parameter this, the second parameter arguments
12}
13 function calSum2 (num1, num2 ){
14 return sum. apply (this, [num1, num2]); // The first parameter this, and the second parameter is the parameter Array
15}
16 alert (callSum1 (10, 10); // 20
17 alert (callSum2 (10, 10); // 20

1 // change function Scope
2 window. color = "red ";
3 var o = {color: "blue "};
4 function sayColor (){
5 alert (this. color );
6}
7 sayColor (); // red
8 sayColor. call (this); // red
9 sayColor. call (window); // red
10 sayColor. call (o); // blue

 

 

From Sunday walk