Scope life cycle.
There are a = 10;
function m1(){
There are a = 5;
alert(a);
}
Parameter (formal parameter) and arguments (actual parameters) significant difference
There are a = 10;
var x = 0;
function fn(x){
x =a + 10;
}
fn (a);
Recursive usage
What is recursion?
Their calls itself!
function pr(){
Return Q ()
}
key point:
1. termination condition
2. operation rule
function pr(n){
if (n == 1) {// termination condition
return n;
}
Return not Q (n-1) +;
}
Print any number of hello world;
function pr(n){
if(n==0){
return
}
document.write('hello world!!<br>');
Return Q (n-1);
}
per (10)
Case: find n numbers and, 5 calculates 1 + 2 + 3 + 4 + 5
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<body>
</body>
<script type="text/javascript">
// function declaration
function getSum(x) {
if (x == 1) {
return 1;
}
return x + getSum(x - 1);
}
// call the function
console.log(getSum(5));
</script>
</html>
案例：输出斐波那契额数列数列的前20项(递归)
斐波那契数列指的是这样一个数列 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233，377，610，987，1597，2584，4181，6765，10946，17711，28657，46368........
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<body>
</body>
<script type="text/javascript">
function fib(n) {
if (n == 1 || n == 2) {
return 1
}
return fib(n - 1) + fib(n - 2)
}
for (var i = 1; i <= 20; i++) {
document.write(fib(i) + '<br>')
}
</script>
</html>