【程式碼筆記】Web-JavaScript-JavaScript 型別轉換
阿新 • • 發佈:2019-01-07
一,效果圖。
二,程式碼。
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>JavaScript 型別轉換</title> </head> <body> <!--typeof操作符--> <p> typeof 操作符返回變數、物件、函式、表示式的型別。</p> <p id="demo"></p> <script> document.getElementById("demo").innerHTML = typeof "john" + "<br>" + typeof 3.14 + "<br>" + typeof NaN + "<br>" + typeof false + "<br>" + typeof [1, 2, 3, 4] + "<br>" + typeof { name: 'john', age: 34 } + "<br>" + typeof new Date() + "<br>" + typeof function() {} + "<br>" + typeof myCar + "<br>" + typeof null; </script> <!--constructor 屬性--> <p>constructor屬性返回變數或物件的建構函式.</p> <p id="demo1"></p> <script> document.getElementById("demo1").innerHTML = "john".constructor + "<br>" + (3.14).constructor + "<br>" + false.constructor + "<br>" + [1, 2, 3, 4].constructor + "<br>" + { name: "john", age: 34 }.constructor + "<br>" + new Date().constructor + "<br>" + function() {}.constructor; </script> <!--constructor 屬性--> <p>判斷是否為陣列。</p> <p id="demo2"></p> <script> var fruits = ["Banana", "Orange", "Apple", "Mango"]; document.getElementById("demo2").innerHTML = isArray(fruits); function isArray(myArray) { return myArray.constructor.toString().indexOf("Array") > -1; } </script> <p>判斷是否為日期。</p> <p id="demo3"></p> <script> var myDate = new Date(); document.getElementById("demo3").innerHTML = isDate(myDate); function isDate(myDate) { return myDate.constructor.toString().indexOf("Date") > -1; } </script> <p>String()方法可以將數字轉換為字串</p> <p id="demo4"></p> <script> var x = 123; document.getElementById("demo4").innerHTML = String(x) + "<br>" + String(123) + "<br>" + String(100 + 23); </script> <p>toString()方法將數字轉為字串</p> <p id="demo5"></p> <script> var x = 123; document.getElementById("demo5").innerHTML = x.toString() + "<br>" + (123).toString() + "<br>" + (100 + 23).toString(); </script> <p> typeof 操作符返回變數或表示式的型別。</p> <button onclick="myFunction()">點我</button> <p id="demo6"></p> <script> function myFunction() { var y = "5"; var x = +y; document.getElementById("demo6").innerHTML = typeof y + "<br>" + typeof x; } </script> <p>typeof操作符返回變數或表示式的型別</p> <button onclick="myFunction()">點我</button> <p id="demo7"></p> <script> function myFunction() { var y = "john"; var x = +y; document.getElementById("demo7").innerHTML = typeof + "<br>" + x; } </script> </body> </html>
參考資料:《菜鳥教程》