Determine the data type of the variable:
##typeof()
In addition: null, object, and array will all return "object".
<!DOCTYPE HTML> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>php.cn</title> <script> var x1 = "abc"; //string var x2 = 110; //number var x3 = true; //boolean var x4; //undefined var x5 = null; //object //使用typeof()判断变量的数据类型 var result = typeof(x5); //输出变量的类型和结果 document.write(x5+"的数据类型为："+result); </script> </head> <body> </body> </html>
Note: You can try to determine the data types of several other variables
##Extract integers and floating point numbers from strings
Function: Extract integers from left to right in a string. If non-integer content is encountered, the extraction is stopped and the result is returned.
Note: If the first character is a non-integer, it will stop immediately and return NaN.
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>php.cn</title>
<script>
document.write(parseInt("500eps")+"<br/>");
document.write(parseInt("500.88")+"<br/>");
document.write(parseInt("a120px")+"<br/>");
</script>
</head>
<body>
</body>
</html>parseFloat() system function, global functionFunction: Extract floating point types from left to right in a string; encounter non-floating point types content, stop extracting and return the result.
Note: If the first character is a non-floating point type, it stops immediately and returns NaN.
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>php.cn</title>
<script>
document.write(parseFloat("500eps")+"<br/>");
document.write(parseFloat("500.88")+"<br/>");
document.write(parseFloat("a120px")+"<br/>");
</script>
</head>
<body>
</body>
</html>