JavaScript (ii)--grammar

1. Basic data type:

String, Decimal, Integer, DateTime, Boolean, and so on.

2. type conversion:

It is divided into automatic conversion and casting, which is generally used for casting.

Other types are converted to integers: parseint ();

Other types convert to decimals: parsefloat ();

Determine if it is a valid number type: IsNaN ();

is a number then returns false, not a number to return ture.

Example:

var a =prompt ("Please enter a number", "can only be a number!! "); if (a!=null) {    var b =IsNaN (a);     if (b==false)    {        alert ("input correct! ")        }    else    {        alert (" Input Error!! ")        }}</script>

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3. operators:

Math operator : +-*/% + +-;

relational operators : = =! = >= <= > <;

logical operator :&& | | ！ ；

Other operators : + = = *=/=%=? ：；

4. statement:

It is generally divided into sequential, branching, and cyclic statements.

( 1 ) Branch Statements if :

if (judging condition)

{

Statements that meet the criteria to be executed

}

Else

{

Statements executed when a condition is not met

}

( 2 ) Loop for statement:

for (initial condition; cyclic condition; state change)

{

Loop body

}

(3) Problem type: exhaustive, iterative.

(4) Two keywords: break and continue.

(5) If you want to output the value of a parameter: the value of the output is "+a+" and "+b"

5. Variables:

are generic type Var, can store other types of values, can be used directly, not defined. But it's customary to define.

Defining variables: var A; //All variable definitions are defined with Var, var is a generic mutable type.

var s = "3.14"; var n = parsefloat (s);; s + = 5;
var d = parseint (s);

6. Arrays:

Definition of the array: new Array (); //Its length is dynamically variable and can be placed in any type of element.

Assignment of array elements: a[0]=123;  a[1]= "Hello"; the index in the//element starts at 0.

The value of the array: A[i];

Array properties: A.length; the number of elements in the//array, length.

Methods: A.sort (); //array sorting, sorted by the first character of each element.

A.reverse (); //Flip an array.

7. functions:

Four elements of a function: name, input, return value, processing.

Define functions: Function add (formal parameter) {function body} //function named Add, input as parameter, return value can be var type, or return value.

The function must be called to execute. Call to function: Add (argument).

Example:

1. Enter your gender, height, and weight to see if the criteria are met

2. Enter your name, score, check whether the pass, if >=80, and then output you are excellent! Continue to maintain

3. Set up a DIV, prepare 3 images, set 3 buttons, change the different backgrounds, the default is the first (similar to the QQ Space Change theme)

4. Set a P tag, and when you click the position of the P tag, change the color of the text, change the size of the text

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 transitional//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">font{Font-weight:700;}</style>Sex (male/female): <input id= "Sex" type= "text"/><br/> Height (cm): <input id= "height" type= "text"/><br/>weight (kg):<input id= "Weight" type= "text"/><br/><input type= "button" value= "Check whether standard" onclick= "Check ()"/>< br/><br/><font size= "+3" >2. Enter your name, score, check whether the pass, if >=80, then output you are very good! Continue to keep </font><br/>Name:<input id= "name" type= "text"/><br/>Score:<input id= "Score" type= "text"/><br/><input type= "button" value= "See if Pass" onclick= "Chakan ()"/>< br/><br/><font size= "+3" >3. Set up a DIV, prepare 3 images, set 3 buttons, change different backgrounds respectively, default is the first (similar to the QQ Space change theme) </font>< BR/><div id= "D" style= "width:360px; height:240px; border:1px solid red; Background-image:url (123.jpg) "></div><br/><input type=" button "onmouseover=" Change1 () "Value=" First theme "/> <input type=" button "onmouseover=" Change2 () "value=" Second topic "/> <input type=" button "onmouseover=" Change3 () "Value=" the third theme "/><br/><br/><font size=" +3 ">4. Set a P tag, change the color of the text when you click the position of the P tag, change the size of the text </font><br/><p id= "P1" onclick= "Color1 ()" > Looking forward, looking forward, the East wind came, spring's footsteps near. </p><p id= "P2" onclick= "Color2 ()" > Everything was just like waking up, and pleasantly opened his eyes. The mountain Lang run up, the water rose up, the sun blushed up. </p><p id= "P3" onclick= "Color3 ()" > Grass secretly from the land drilling out, tender, green and green. In the garden, in the fields, look, a big big one. Sit, lie down, play two roll, kick a few kicks, race a few times to run, catch a few mystery. The wind is soft, the grass is limp. </p></body>functionCheck () {varSex = document.getElementById ("Sex"). Value; varHeight = parseint (document.getElementById ("height")). Value); varWeight = parseint (document.getElementById ("Weight"). Value); if(sex== "Male")    {        if(weight) {alert ("The weight is thin, eat a bit more!" "); }        Else if(weight>height-100+3) {alert ("You are too fat, exercise more!" "); }        Else{alert ("Weight is standard, keep it up!" ")    ; }        }        Else if(sex== "Female")    {        if(weight) {alert ("The weight is thin, eat a bit more!" "); }        Else if(weight>height-110+3) {alert ("You are too fat, exercise more!" "); }        Else{alert ("Weight is standard, keep it up!" ")    ; }            }    Else{alert ("Is it a man or a woman?" "); }}functionChakan () {varName = document.getElementById ("name"). Value; varScore = parsefloat (document.getElementById ("Score"). Value); if(Score>=0 && score<=100)    {        if(score<60) {Alert (name+ "Failed"); }        Else        {            if(score>=80) {alert ("Congratulations," +name+ ", passed, and you are excellent, continue to keep! "); }            Else{alert (name+ "Passed"); }        }    }    Else{alert ("Score input is wrong!" "); }}functionChange1 () {varD = document.getElementById ("D"); D.style.backgroundimage= "url (123.jpg)";}functionChange2 () {varD = document.getElementById ("D"); D.style.backgroundimage= "url (213.jpg)";}functionChange3 () {varD = document.getElementById ("D"); D.style.backgroundimage= "url (312.jpg)";}functionColor1 () {varP1 = document.getElementById ("P1"); P1.style.color= "#3F3"; P1.style.fontSize= "30px"; }functionColor2 () {varP2 = document.getElementById ("P2"); P2.style.color= "#FF3"; P2.style.fontSize= "30px"; }functionColor3 () {varP3 = document.getElementById ("p3"); P3.style.color= "Red"; P3.style.fontSize= "30px"; }</script>

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Run the effect shows here is not attached, interested in the words copy the code, run the following to see your own.

Note: * can be read on the head (first read the head)

The page is automatically refreshed when the form is submitted, preferably turned off

Writing:

1. Output

<script>

document.write ("Hello World");

</script>

2. Button Application

<input name= "alert" value= "alert" type= "button" onclick= ' Alert ("This is the trigger event") '/>

3. Define variables and output

var Bianliang;

Bianliang= "123";

document.write (Bianliang);

4. Changing the attributes of an element

<p id= "Hello" >hello</p>

<script>

function Hello ()

{

X=document.getelementbyid ("Hello")

X.style.color = "#ff0000";

}

</script>

<input type= "button" value= "Click to change Color" onclick= "hello ()"/>

<!--click From Black to red--

5 , Item index, indicating the first N an element that appears, with the Getelementsbyname simultaneous use

6. Define a set of variables

var student =

{

Name: "Zhang San",

Sex: "Male"

};

Student.name= "Zhang San";

document.write (Student.name);

(* print "Zhang San")

7. External Call JS

<script src= "" ></script>

JavaScript (ii)--grammar