JavaScript Beginner Chapter _4 (loops and Functions)

seven, Circular Statements
1.While
Grammar:

 while (exp) {     //statements;}

Description

 while (variable <= End Value) {     

Cases:

var i=0;  while (i<=9) {        // use a loop to output 9 photos on the page    document.write (' );        I+ +;      }

2. do...while

The Do...while function is the same as while, except that the do...while is executed after the execution, while Vice Versa.

syntax:

 do {     //statements;}  while (condition);

Description

 do {     while (variable <= end value);

Cases:

var i=0;  do {     // using loops to output 9 photos     document.write ('  " );     I+ +;}  while (i<=9);

3.for Loop Statement
Grammar:

 for (initial; expression; post-loop-expression) {    //}

Description

 for (variable = start value; variable <= end value; variable = variable + step value) {     

Cases:

4. Break statement and Continue statement

The break statement can exit the Loop immediately;
the continue statement simply exits the current loop;
Cases:

 for (var i = 1; i < i++) {     if(i = = 4) {         continue//  Exit the loop, and the remaining loop continues to execute         }     if(i = = 7)        {break;    // terminates the loop, after which the remaining loops are not executing     }    

seven, function

description: A function is a set of statements that completes a function, defined by a keyword function + function name + a set of parameters; function in a fixed

After righteousness can be repeated calls, often used to write functions as a function, the use of functions can make the structure of the code more clear.
1. Basic Syntax:

function funname (arg0, arg1, ... argN) {     //}

Use of 2.return

Return a value from a function using the return statement

function sum (num1, num2) {     return num1 +var s = Sum (1, 2); alert (s);      // result is 1+2=3;

Attention:

1. Any code that is behind the return statement will never be executed!
2. In javascript, you don't have to specify a return value!
3. When defining the parameters of a function, if the function is called without passing arguments, it does not give an error, but it can be judged in the function whether there is a pass-in argument, for example:

if (variable = = 'undefined ' | | variable = = Null) {         variable= ' 1 ';    //can give him a default value }

JavaScript Beginner Chapter _4 (loops and Functions)