JavaScript: Type Conversion
1、Display the typeof all variables types
<!DOCTYPE html> <html> <body> <h2>The JavaScript typeof Operator</h2> <p>The typeof operator returns the type of a variable, object, function or expression.</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> </body> </html>
string
number
number
boolean
object
object
object
function
undefined
object
2、convert a number to a string.
<!DOCTYPE html> <html> <body> <h2>The JavaScript String() Method</h2> <p>The String() method can convert a number to a string.</p> <p id="demo"></p> <script> var x = 123; var y = 453; document.getElementById("demo").innerHTML = String(x) + "<br>" + (y+y) + "<br>" + (y+y.toString()) + "<br>" + y+y + "<br>" + String(123) + "<br>" + String(100 + 23); </script> </body> </html>
3、find out if a variables is an Array.
<!DOCTYPE html> <html> <body> <h2>JavaScript Arrays</h2> <p>This "home made" isArray() function returns true when used on an array:</p> <p id="demo"></p> <script> var fruits = ["Banana", "Orange", "Apple", "Mango"]; document.getElementById("demo").innerHTML = isArray(fruits); function isArray(myArray) { console.info(myArray.constructor) //function Array() { [native code] } return myArray.constructor.toString().indexOf("Array") > -1; } </script> </body> </html>
<script> var myDate = new Date(); document.getElementById("demo").innerHTML = isDate(myDate); function isDate(myDate) { return myDate.constructor.toString().indexOf("Date") > -1; } </script>