Program composition of JavaScript tutorial

The basic structure of JavaScript scripting language is composed of control statements, functions, objects, methods, properties, etc., to implement programming.

Program control flow

In any language, program control flow is necessary. It can reduce the confusion of the entire program and make it execute smoothly in a certain way. The following are commonly used program control flow structures and statements in JavaScript:

1. if conditional statement

Basic format:

if (expression) {

Statement segment 1;

...

} else {

Statement segment 2;

....

}

Function: If the expression is true, execute statement segment 1; otherwise, execute statement segment 2.

2. For loop statement

Basic format:

for (initialization; condition; increment)

statement set;

Function: implement conditional loop, when the condition is established, execute the statement set, otherwise jump out of the loop body.

Explanation: The initialization parameter tells the starting position of the loop and must be assigned the initial value of the variable.

Condition: It is the condition used to determine when the loop stops. If the condition is met, execute the loop body, otherwise jump out.

Increment: Mainly defines how the loop control variable changes each time it loops. The three main statements must be separated by commas.

3. while loop

Basic format:

while (condition)

statement set;

This statement is the same as the For statement. When the condition is true, repeat the loop, otherwise exit the loop.

For and while statements

Both statements are loop statements. Using the For statement is easier to understand and more compact when processing related numbers; while the while loop has a more special effect on complex statements.

4. The break and continue statements

are the same as the C++ language. Use the break statement to make the loop jump out of For or while, and continue to skip the remaining statements in the loop and enter the next loop.

Function

Function provides programmers with a very convenient ability. Usually when designing a complex program, the program is always divided into some relatively independent parts according to the functions to be completed, and a function is written for each part. Thus, each part is fully independent, has a single task, and the program is clear, easy to understand, easy to read, and easy to maintain. JavaScript functions can encapsulate modules that may be used multiple times in a program. And can be called as a result of event-driven procedures. Thereby implementing a function to associate it with the event driver. This is different from other languages.

1. JavaScript function definition

Function function name (parameters, variables) {

function body;.

Return expression;

}

Note: When calling a function, any variable or literal can be used Passed as arguments.

Function is defined by the keyword Function.

Function name: Define the name of your own function.

The parameter list is the value passed to the function for use or operation. Its value can be a constant, variable or other expression.

Call a function by specifying the function name (actual parameters).

Must use Return to return the value.

Function names are case-sensitive.

2. Formal parameters in the function

In the definition of the function, we see that there is a parameter list after the function name. These parameter variables may be one or several. So how can we determine the number of parameter variables? In JavaScript, you can check the number of parameters through arguments.Length.

Example:

Function function_Name(exp1,exp2,exp3,exp4)

Number = function _Name.arguments.length;

if (Number>1)

document.wrile(exp2);

if (Number& gt ; 2)

document.write (exp3);

if (number & gt; 3)

document.write (exp4);

...

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