Detailed introduction to the three major structures of javascript development tutorial

What I bring to you this time is the analysis of the three major structures of the program in the JS development tutorial. We know that the program has a sequential structure, a selection structure and a loop structure. This article will give you a good analysis.

The three major structures of the program

Sequential structure

The sequential structure means that the operations in the program are executed in the order in which they appear.

Selection structure

The selection structure indicates that there are branches in the processing steps of the program, and it needs to select one of the branches for execution based on a specific condition. There are three types of selection structures: single selection, double selection and multiple selection.

Loop structure

The loop structure means that the program repeatedly performs one or more operations until a certain condition is false (or true) before the loop can be terminated. The most important thing in the loop structure is: under what circumstances is the loop executed? Which operations need to be executed in the loop?

Statement

ECMA-262 specifies a set of statements (also called flowControl Statement). In essence, statements define the main syntax in ECMAScript, and statements typically use one or more keywords to accomplish a given task. The statement can be simple, such as notifying a function to exit; it can also be more complex, such as specifying the number of times a command should be repeated.

Conditional statements: Think of the code in javascript as branch paths.

Loop statement: It is a loop in the program path, which allows a part of the code to be executed repeatedly.

The single branch structure of the program IF statement

The most commonly used statement in most programming languages ​​ is the if statement. The following is the syntax of the if statement:

if (condition) { Statement 1 } else { Statement 2 }

The condition can be any expression; and the result of evaluating this expression Not necessarily a Boolean value.

ECMAScript will automatically call the Boolean() conversion function to convert the result of this expression into a Boolean value. If the condition evaluates to true, statement 1 is executed, and if the condition evaluates to false, statement 2 is executed. And these two statements can be either a line of code or a code block (multiple lines of code enclosed in a pair of curly braces).

Three formats of if statements:

1, if (condition) { statement 1 }

2, if ( condition) { statement 1 } else { statement 2 }

3. if (condition) { statement 1 } else if ( condition) { statement 2 }...else{ statement }

Multi-branch structure of the programswitch statement\break statement

The switch statement is most closely related to the if statement, and it is also a flow control statement commonly used in other languages.

switch (expression) {

case value: statement block; break;

case value: statement block; break;

case value: statement block; break;

......

default: statement block

}

switch Each case in the statement The meaning is: "If the expression is equal to this value (value), execute the following statement (statement)." The break keyword will cause the code execution flow to jump out of the switch statement. If the break keyword is omitted, execution of the next case will continue after the current case is executed. The final default keyword is used to execute automatic code (therefore, it is equivalent to an else statement) when the expression does not match any of the previous situations.

# I believe you have mastered the method after reading the above introduction. For more exciting information, please pay attention to other related articles on the php Chinese website!

Related reading:

Implementation steps of DOM programming in html5

How to use events in HTML

Detailed introduction and compatibility processing of the progress element in HTML5

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