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Học JavaScript qua ví dụ part 18

Đệ quy Nghĩa của đệ quy: đệ quy: Xem đệ quy. Định nghĩa này nói rằng tất cả! JavaScript hỗ trợ đệ quy. Vì vậy, nó là gì? Bạn đã bao giờ được tháo rời một con búp bê Nga? Mở con búp bê ra ngoài và có một bản sao nhỏ hơn búp bê bên trong nó, mất rằng một trong ra ngoài, và bạn thấy khác, và như vậy, cho đến khi bạn có thể giảm đến một con búp bê nhỏ ở cuối. | 7.1 What Is a Function 161 Figure 7.14 The closure remembers the values of local variables. 7.1.5 Recursion Definition of recursion recursion See recursion. This definition says it all JavaScript supports recursion. So what is it Have you ever taken apart a Russian doll Open up the outside doll and there s another smaller duplicate doll inside it take that one out and you find another and so on until you get down to a tiny doll at the end. Then when you put them back you start with the last doll you opened and keep returning each doll until you get back to the first one you opened. A recursive function is a function that calls itself. It s a chain of function calls to the same function. The first time it calls itself is the first level of recursion the second time is the second level and so on. When a function calls itself execution starts at the beginning of the function and when the function ends the program backs up to where it was when it called the function and starts executing from that point. Most important there must be a way to stop the recursion or it will be infinite and probably cause the program to crash. An example often used to describe recursion can be demonstrated with a function to produce a Fibonacci sequence of numbers 0 1 1 2 3 5 8 13 21 34 55 and so on. Here is a little bit of history about how this formula was derived. In the beginning of the 13th century an Italian mathematician Leonardo Fibonacci was trying to solve the following problem presented at a mathematical competition in Pisa How many rabbits would be produced in a year if beginning with a single pair of rabbits every month each pair reproduces a new pair of rabbits which become productive when they are one month old and none of them die and so on Fibonacci came up From the Library of WoweBook.Com 162 Chapter 7 Functions with a formula named after himself to answer the rabbit question. The sequence starts with 0 and 1 and then produces the next number by adding the two previous .