JavaScript ???? ?? ??
? ???? JavaScript ??? ?? ??? ?? ?????.
??? ???
???? ?? ??? ??? ?? ???? ??? ???? ?? ?????. ??? ??? ????.
string.replace(subStr/reg,replaceStr/function)
?? ????? ?? ??? ?? ????? ? ?? ????? ??? ??? ?? ??????.
"I'm Byron".replace("B", "b") /? ??? ? ????. / I'm byron
??? ????
"?? ???? ????".replace("n","N") //?? ?????. , and you?
??? ???? ??? ?? ? ?? 'n'? ???? ?????. ???? ???? ?? ???? ?? ? ?? ??? ???? ? ??? ???? ??? ?????. ???? ??? ?? ???? RegExp ??? ???? ?? ?? ??? ???? ???.
"?? ???? ???".replace(/n/g,"N") // ?? ???? ???
typeof
typeof? ?? ?? ?? ??? typeof? ??? ??? ????? ????. ?, ??? ??? ??? ? ??? ??? ??? ??? ?? ?? ??? ? ??? ????
typeof 1; //numbertypeof( 1); //number, ??? ??? ??? ??? ????. ???? ?? typeof? ?? ?? ??????. ??? ??? ?? ??? ?????. ??? ? ?? ??? ??? ????. JavaScript?? ??, ???, ??, ???? ?? ? ?? ? ?? ?? ?? ??? ??? ?? ?? ????.
typeof 123; //??
typeof NaN //??
typeof "123" //string
typeof false; //boolean
typeof ???? ??;
typeof null //object
typeof new Array(); //object
typeof (new Array()); //???? ??? ???? ??? ???? ???. , ??? ?????
typeof (function(){}) / /function
typeof a; //undefine
1? ???? ??? ?????
2. NaN? ??? ???? ???? typeof? ??? ??? ?????
3. "123"? ???? ??? ???? ?????.
4. false ??? boolean
5???. ???? ?? ?? ? ?? ??? "???? ??" ??? ? ??? ?? ? ????
6. null ??? null? ??? ????? typeof? null
7? ???? ? ??? ??? ??? ????. ?? ??? ???? ?? ??? Array ?? Date
? ???? ?? ??9. ??? ?? ????? ??? ?? ???? ???. ??? typeof? ?? ??? ???? ??? ?????
10. ???? ?? ??? javascript?? undefine
if ? ==
? ?????. Boolean? true ?? false? ???? ??? ??? 0, Nan, "", Undefine, NULL, FALSE? ?? false? ?????
(! False) {
console.log (1)
(!"") {
? ? ? ? ? ? ? console.log(3 };
?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?????????????????????????????? ?123456? ??? ?????
??? ?? ??? ?? ??==false0==false; //true
"0"==false; //true, ??? true?? ??? ????. = false //false
null==false //false
null==null //true
NaN==NaN //false
null==???? ?? //true
?? ??? ?? ?? JavaScript ?????? if ???? ?? ???? ??(=)? ???? ??? ??? ?????. ??? ??? ?? ???? ?? ? ?? ???? ????. ( ==). x? 10? ??? ??? ???? false? ???? ??(??? ??): ?? ???? ???? ?? ??? ?? ???? ===? ?? ????? ?????. ??? ???? ?? ??? ?? ?? if ???? false? ?????. ?? ??? ??? ??? ?? ?? ???(===)? ???? ??? ??? ?? ????? ?? ? ??? ???? ?? ?? ???? ???? ????: ??? ??? ?? ???? ??? ? ?? ??? ??? ????. ??? ? ???? ???? ????. JavaScript? ???? ?? ??? + ???? ?????. ???? ??? ?? ? ??? ??? ?? ??? ???? ???? ?? ???? ? ? ????. var x = 10 + 5 // x? ??? 15 ????? ??? ?? ? ???? JavaScript? ?? ???? 64?? ????? ???(float)? ?????. JavaScript? ??? ?? ????? ??? ?? ??? ???? ???? ???? ?????. var x = 0.1; Return ? ?? ? ???? JavaScript? ????? ??? ??? ??? ???? ?????. ?? ?? ??? ???? ?? ??? ?????. ? ?? ??? ???? ???? JavaScript??? ?? 4? ??? ?? ??? ???? ?????. function myFunction(a) { parse ??? ?? ???? ?? ??: var JavaScript? ?? ? ?? ?? ???? ?????. power = 10; ??? A?? ??? ?? ?? ???????. return JavaScript? ???? ?? ????. return; JavaScript?? ????? ?? ?????. return? ??? ???? JavaScript? return ?? ????. ??? ???? ??? ?? ?? ?? ????? ????? ??? ??? ???? ??? ? ????. ??? ???? ???? ??? ?? ??(?? ??)??? ???. JavaScript? ?? ??? ??? ???? ?? ???? ??? ?? ??? ?????. var person = []; JavaScript?? ??? ??? ???? ?????. ??? ???? ???? JavaScript? ??? ???? ? ??? ?? ??? ??????. ? ??? ??? ??? ??? ???? ??? ? ?? ???? ????. ??? ??? ??? ?????: var person = []; ??? ?? ??: ??? ?????. ?? ??? ??? ? ????. ??? ??: ???? ?? ?? Null? ???? JavaScript??? ??? null? ???? ??, ?? ? ???? ???? ?? ?? ?????. ??? ??? ???? null? ? ???, ??? ??? ???? ????. ??? ????? ?????? ?? ??? ?? ???? ??? ??? ?????. ??? ?? ??: if (myObj !== null && typeof myObj !== "undefine") ??? ??? ??? ?????? ???? ?? ?? typeof? ???? ??? ????. : if (myObj ?? !== "???? ??" && myObj !== null) <!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文網(wǎng)(php.cn)</title>
</head>
<body>
<p id="demo"></p>
<script>
var x = 0;
document.getElementById("demo").innerHTML = Boolean(x == 10);
</script>
</body>
</html><!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文網(wǎng)(php.cn)</title>
</head>
<body>
<p id="demo"></p>
<script>
var x = 10;
var y = "10";
document.getElementById("demo").innerHTML = Boolean(x === y);
</script>
</body>
</html><!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文網(wǎng)(php.cn)</title>
</head>
<body>
<p id="demo"></p>
<script>
var x = 10;
switch(x) {
case "10": alert("Hello");
}
</script>
</body>
</html>
var x = 10 + "5" // x? ??? "105"???
var y = 0.2;
var z = x + y // z? ??? 0.3???.
if (z == 0.3) //Return false<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>php中文網(wǎng)(php.cn)</title>
</head>
<body>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = myFunction(55);
function myFunction(a) {
var
power = 10;
return
a * power;
}
</script>
</body>
</html>
var
power = 10;
return; // ?????? ??? undefine
a * power;
}? ?????.
person[0] = "John";
person[1] = "Doe";
person[2] = 46;
var x = person.length return; 3
var y = person[0]; // person[0]? "John"? ?????
person["firstName"] = "John";
person[ "lastName"] = "Doe";
person["age"] = 46;
var x = person.length;
??? ?? ??:
??? ?? ??:
