ES02 變量、數組、對象、方法
阿新 • • 發佈:2018-03-24
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1 變量
1.1 變量的聲明
利用var關鍵字來聲明變量,例如:
var a = 100;
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title>JavaScriptTest</title> <meta name="description" content=""> <meta nameView Code="keywords" content=""> <link href="" rel="stylesheet"> <!-- <script src="/js/jquery.js"></script> --> <script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script> <script> var a = 100; function test01() { alert("變量a的值為:" + a); }</script> </head> <body> <p id="testP">Hello Boy</p> <button id="test" onClick="test01()">測試按鈕</button><br /> <script> </script> </body> </html>
1.2 變量的作用域
1.2.1 局部作用域
在函數中聲明的作用域叫做局部作用域
1.2.2 全局作用域
在函數之外聲明的作用與叫做全局作用域
1.2.3 區別
局部作用域中可以獲取全局變量,但是局部變量只能在局部作用域中使用,即:局部變量只能在聲明它的方法中使用
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title>JavaScriptTest</title> <meta name="description" content=""> <meta name="keywords" content=""> <link href="" rel="stylesheet"> <!-- <script src="/js/jquery.js"></script> --> <script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script> <script> var a = "全局變量a"; function test01() { var b = "局部變量b"; alert("test01方法 -> " + a); alert("test01方法 -> " + b); } function test02() { alert("test02方法 -> " + a); alert("test02方法 -> " + b); } </script> </head> <body> <p id="testP">Hello Boy</p> <button id="test01" onClick="test01()">測試按鈕01</button><br /> <button id="test02" onClick="test02()">測試按鈕02</button> <script> </script> </body> </html>View Code
坑01:在局部作用域中如果使用的變量未i進行聲明操作就會到全局中去尋找對應的全局變量,如果沒找到就會創建一個全局變量
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title>JavaScriptTest</title> <meta name="description" content=""> <meta name="keywords" content=""> <link href="" rel="stylesheet"> <!-- <script src="/js/jquery.js"></script> --> <script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script> <script> var a = "全局變量a"; function test01() { b = "Hello Boy" alert("test01方法 -> " + a); alert("test01方法 -> " + b); } function test02() { alert("test02方法 -> " + a); alert("test02方法 -> " + b); } </script> </head> <body> <p id="testP">Hello Boy</p> <button id="test01" onClick="test01()">測試按鈕01</button><br /> <button id="test02" onClick="test02()">測試按鈕02</button> <script> </script> </body> </html>View Code
2 數組
2.1 數組的聲明
2.1.1 利用 Array 對象進行聲明
var list01 = new Array();
2.1.2 利用 [ ] 進行聲明
var list01 = [];
2.2 數組的賦值
數組名[數組元素索引]
list01[0] = "warrior";
list01[4] = "fury";
坑01:中間為進行初始化的數組元素自動賦值為 undefined
2.3 數組的聲明和賦值
2.3.1 利用 Array 對象實現
var list01 = new Array("warrior", "fury", "重慶火鍋");
2.3.2 利用 [ ] 實現
var list01 = ["warrior", "fury", "重慶火鍋", "小面"];
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title>JavaScriptTest</title> <meta name="description" content=""> <meta name="keywords" content=""> <link href="" rel="stylesheet"> <!-- <script src="/js/jquery.js"></script> --> <script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script> <script> var list01 = ["warrior", "fury", "重慶火鍋", "小面"]; function test01() { for (var i = list01.length - 1; i >= 0; i--) { console.log(list01[i]); } } function test02() { } </script> </head> <body> <p id="testP">Hello Boy</p> <button id="test01" onClick="test01()">測試按鈕01</button><br /> <button id="test02" onClick="test02()">測試按鈕02</button> <script> </script> </body> </html>View Code
3 對象
3.1 對象的聲明
3.1.1 利用 Object
var obj = new Object()
3.1.2 利用 { }
var obj = {};
3.2 對象的賦值
obj.name = "warrior";
obj.address = "重慶市";
3.3 對象的聲明和賦值
3.3.1 利用Object
var obj = new Object({ name: "warrior", address: "重慶", age: 123 });
3.3.2 利用 { }
var obj = { name: "warrior", address: "重慶" };
4 方法
function onCompute() { alert("hello boy"); var a = document.getElementById("a"); var b = document.getElementById("b"); document.getElementById("result").value = Number(a.value) + Number(b.value); }
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title>JavaScriptTest</title> <meta name="description" content=""> <meta name="keywords" content=""> <link href="" rel="stylesheet"> <!-- <script src="/js/jquery.js"></script> --> <script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script> <script> function onCompute() { alert("hello boy"); var a = document.getElementById("a"); var b = document.getElementById("b"); document.getElementById("result").value = Number(a.value) + Number(b.value); } function test01() { } function test02() { } </script> </head> <body> <input type="number" id="a" placeholder="加數01" /> <span> + </span> <input type="number" id="b" placeholder="加數02" /> <span> = </span> <input type="number" id="result" placeholder="結果" /> <button id="compute" onclick="onCompute()">計算</button> <hr /> <button id="test01" onClick="test01()">測試按鈕01</button><br /> <button id="test02" onClick="test02()">測試按鈕02</button> <script> </script> </body> </html>View Code
4.1 有參方法
坑01:由於JavaScript是動態類型語言,所以在定義方法時的形參不用指定類型,用合法的變量名指明就行啦
function test01(a, b) { alert(a); alert(b); }
4.2 帶返回值的方法
function test02(a, b) { alert(test03(a, b)); } function test03(a, b) { return a + b; }
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <title>JavaScriptTest</title> <meta name="description" content=""> <meta name="keywords" content=""> <link href="" rel="stylesheet"> <!-- <script src="/js/jquery.js"></script> --> <script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script> <script> function onCompute() { alert("hello boy"); var a = document.getElementById("a"); var b = document.getElementById("b"); document.getElementById("result").value = Number(a.value) + Number(b.value); } function test01(a, b) { alert(a); alert(b); } function test02(a, b) { alert(test03(a, b)); } function test03(a, b) { return a + b; } </script> </head> <body> <input type="number" id="a" placeholder="加數01" /> <span> + </span> <input type="number" id="b" placeholder="加數02" /> <span> = </span> <input type="number" id="result" placeholder="結果" /> <button id="compute" onclick="onCompute()">計算</button> <hr /> <button id="test01" onClick="test01(‘warrior‘, ‘重慶‘)">測試按鈕01</button><br /> <button id="test02" onClick="test02(1, 2)">測試按鈕02</button> <script> </script> </body> </html>View Code
ES02 變量、數組、對象、方法