<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title>js 基礎(chǔ)</title>
<script type="text/css" src="xxx.js"></script> <!--外鏈?zhǔn)?-->
</head>
<body>
<p onclick="alert('我是行內(nèi)式')">你好</p>
<script type="text/javascript"> //內(nèi)嵌式
// 輸出語(yǔ)句
alert("我是內(nèi)嵌式");
prompt("請(qǐng)輸入：");
confirm("你好嗎？");
console.log("我是控制臺(tái)輸出");
console.error("我是錯(cuò)誤");//了解
console.warn("我是警告");//了解
document.write("<h1>我是h1標(biāo)簽</h1>");//頁(yè)面輸出內(nèi)容而且識(shí)別標(biāo)簽
//數(shù)據(jù)類(lèi)型
var str1 = "aa";
var str2 = "123";
var num = 123;
var bool = true; //true false
var kong =null;
var wu ; //undefined 未定義
//查看數(shù)據(jù)類(lèi)型 (typeof 變量 )
var type = typeof(str1);
//類(lèi)型轉(zhuǎn)換 成數(shù)字number
var str = "123.2a";//字符串類(lèi)型的數(shù)字
var bool = true;
var num1 = parseInt(str); //取第一部分?jǐn)?shù)字 并取整 沒(méi)有數(shù)字Nan 輸出：123
var num2 = parseFloat(str); //取第一部分?jǐn)?shù)字 保留小數(shù) 輸出：123.2
var num3 = Number(str); //有非數(shù)字就會(huì)報(bào) Nan 沒(méi)有就全部轉(zhuǎn)換成數(shù)字
console.log(typeof Number(bool)); //boolean 轉(zhuǎn)成1
console.log(typeof (str-0)); //數(shù)子類(lèi)型的字符串在處"+"外都會(huì)有隱士類(lèi)型轉(zhuǎn)換
console.log(typeof (bool-0));
console.log(typeof (str*1));
console.log(typeof (bool*1));
console.log(typeof (str/1));
console.log(typeof (bool/1));
console.log(typeof typeof (bool/1)); //數(shù)據(jù)類(lèi)型是用string定義的
//類(lèi)型轉(zhuǎn)換 成字符串String
var num4 = 123;
var num5 = num+""; //"+"在有字符串在于運(yùn)算的時(shí)候表示拼接 而非相加
var num6 = num.toString();
var num7 = String(num2);
console.log(typeof num5);
//進(jìn)制轉(zhuǎn)換
var num8 = parseInt(111,2); //任意進(jìn)制轉(zhuǎn)換成十進(jìn)制。111：值,2：進(jìn)制 輸出：7
var num = 10;
var renyi = num.toString(16); //十進(jìn)制轉(zhuǎn)換成任意進(jìn)制 輸出：a
//特殊的 undefined 和 null
console.log(undefined == null); //true
console.log(undefined === null); //false
console.log(undefined+10); // Nan 不是一個(gè)數(shù)字
console.log(null+10); //10
//操作符種類(lèi)
一,算數(shù)運(yùn)算符（+—*/...）
a) 一元運(yùn)算符：正號(hào),負(fù)號(hào),++,--,平方等一個(gè)變量就能運(yùn)算
b) 二元運(yùn)算符：+-*/%等兩個(gè)變量才能運(yùn)算
c) 三元運(yùn)算符： 值1？值2：值3；
二,邏輯運(yùn)算符（ ||&& ! ）（或且非）
三,比較運(yùn)算符（<,>,==,>=...）
四,賦值運(yùn)算符（=,+=,-=,*=,/=,%=）
//優(yōu)先級(jí)
1 ()
2 !,-（負(fù)數(shù)）,++,-- （正數(shù)省略+）（一元運(yùn)算）
3 *,/,%
4 +,- （加,減）（二元運(yùn)算）
5 <,<=,<,>= （一級(jí)邏輯運(yùn)算）
6 ==,!=,===,!==, （二級(jí)邏輯運(yùn)算）
7 && （三級(jí)級(jí)邏輯運(yùn)算）
8 ||
9 ?: （三元運(yùn)算）
10 =,+=,-=,*=,/=,%= （賦值運(yùn)算）
// && 和 || 運(yùn)算
一 && 鏈接兩個(gè)boolean類(lèi)型,有一個(gè)是false結(jié)果就是false, A與B
都是true取后面,都是false取前面
二 || 鏈接兩個(gè)boolean類(lèi)型,有一個(gè)是true結(jié)果就是true, A或B
都是true取前面,都是false取后面
</script>
</body>
</html>This article explains the basic data types and conversion base operators of js. For more related content, please pay attention to the PHP Chinese website.
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