?????? ???
JavaScript ???
???? ?????
???? ?? ???? ??? ??? ????. ?? ??? ?? ???(?? ??)? ??? ??? ????? ????? ??? ??? ?????. ???. ???? ??:
1. ?? ??? ?? ??? ?? ?? ? ??????.
2. ???? ??? ??? ? ???? ???? ?? ?? ?????.
??? ??? Javascript? ?? ??? ??? ?????. ?, ?? ??? ?? ???? ?? ??? ?? ??? ?????. ?? ??? ?? ??? ?? ?? ??, ???? ? ?? ??? ???? ?? ??? ??? ?? ?? ??? ???? ? ????. ??? ?? ?? ? ??? ?? ???? ?? ?? ???? ???? ???? ?????.
2. ???? ???? ???? ?? ?? ??
?? JS? ?? ?? ???? ??? ??? ? ????? ?? ???? ???. ?? ???? ???? 5?? ??? ???? ???? ???? ???? ??? ?????. ?? ???? ??? ??? ???????.
//? ?? ?? ??
function Circle(r) {
this.r = r;
}
Circle.PI = 3.14159;
Circle.prototype.area = function() {
return Circle.PI * this.r * this.r;
}
var c = new Circle(1.0);
alert(c.area());? ?? ??? ??? ?? ??? ??? ? ?? ??? ??? ????.
//? ?? ?? ??
var Circle = function() {
var obj = new Object();
obj.PI = 3.14159;
obj.area = function( r ) {
return this.PI * r * r;
}
return obj;
}
var c = new Circle();
alert( c.area( 1.0 ) );? ?? ??? ??? ???? ??? ??? ??? ???? ????.
//? ?? ?? ??
var Circle = new Object();
Circle.PI = 3.14159;
Circle.Area = function( r ) {
return this.PI * r * r;
}
alert( Circle.Area( 1.0 ) );? ??? ?? ? ?????, ? ??? ?? ?? ?? ??? ??? ???? ???? ????.
//??? 4?? ??
var Circle={
"PI":3.14159,
"area":function(r){
return this.PI * r * r;
}
};
alert( Circle.area(1.0) );? ??? ????? ?? ???? ?? ?????. var obj = {}? ? ??? ?????.
//?? ?? ?? ??
var Circle = new Function("this.PI = 3.14159;this.area = function( r ) {return r*r*this.PI;}")
Alert ( (new Circle()).area(1.0) )
??? ?? ? ?? ??? ???? ?? ??? ????? ???.
????? ?? ??? ? 2?? 4?? ? ?? ???, ??? ?? ????? ???.
? ???? JS?? ?? ???? ?????? ???? ?????? ??? ?????? ???????:
var dom = function(){
};
dom.Show = function(){
alert("Show Message");
};
dom.prototype.Display = function(){
alert("Property Message");
};
dom.Display(); //error
dom.Show();
var d = new dom();
d.Display();
d.Show(); //error?? ?? ??
?? ??? ??? ??????. ?, ?? ??? ?? JavaScript ????? ?? ?? ????.
?? ??? ??? ??? ?? ????? ?????. ??? ??? ?? ???? ?? ??? ?????. ??? ????? ????? ?? ???? ?????.
??? ???
? ?? ?? ???? ??? ?? ???? ???? ??? ? ??? ??? ???.
?? ??? ??? ???? ??? ??? ??? ? ????.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<p>全局變量計數(shù)。</p>
<button type="button" onclick="myFunction()">計數(shù)!</button>
<p id="demo">0</p>
<script>
var counter = 0;
function add() {
return counter += 1;
}
function myFunction(){
document.getElementById("demo").innerHTML = add();
}
</script>
</body>
</html>add() ??? ???? ??? ?? ?????.
??? ??? ??? ????. add() ??? ???? ???? ???? ?? ????? ???? ??? ? ??? ????.
?? ??? ???? ???? ??? ???? ??? ??? ?? ??? ? ????.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<p>局部變量計數(shù)。</p>
<button type="button" onclick="myFunction()">計數(shù)!</button>
<p id="demo">0</p>
<script>
function add() {
var counter = 0;
return counter += 1;
}
function myFunction(){
document.getElementById("demo").innerHTML = add();
}
</script>
</body>
</html>? ??? ???? ???? ????. add() ??? ??? ??? ???? ?????. 1?.
JavaScript ?? ??? ???? ? ??? ??? ? ????.
JavaScript ?? ??
?? ??? ?? ??? ??? ? ????.
?? JavaScript??? ?? ??? ? ?? ??? ???? ? ????.
JavaScript? ?? ??? ?????. ??? ??? ?? ??? ?? ??? ??? ? ????.
? ??? ?? ?? plus()? ?? ??? ??? ??? ???? ? ????.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<p>局部變量計數(shù)。</p>
<p id="demo">0</p>
<script>
document.getElementById("demo").innerHTML = add();
function add() {
var counter = 0;
function plus() {counter += 1;}
plus();
return counter;
}
</script>
</body>
</html>???? plus() ??? ???? ? ??? ??? ???? ??? ? ????.
?? counter = 0? ? ?? ????? ?? ???.
??? ??? ?????.
