JS data type conversion and data validity judgment

1. Data type Conversion

parseint () Example:

parseint ("1234blue");//return 1234

parseint ("22.5");//return 22 for integers, the decimal point is an invalid character

parseint ("Blue");//return NaN

Parsefloat () Example:

Parsefloat ("1234blue");//return 1234.0

Parsefloat ("22.34.5");//return 22.34

Parsefloat ("0908");//return 908

Parsefloat ("Blue");//return NaN

Boolean () Example:

Boolean ("");//return false

Boolean ("Hi");//return true

Boolean (+);//return true

Boolean (null);//return false

Boolean (0);//return false

Boolean (New Object ());//return true

Number () Example:

Number (false);//return 0

Number (true);//return 1

Number (undefined);//return NaN

Number (null);//return 0

2. Data validity judgment (e.g. null, empty, etc.)

(1). The NaN property is a special value that represents a non-numeric value, indicating that a value is not a number.

The IsNaN () global function is often used to determine whether a value is a NaN value.

Methods parseint () and parsefloat () return this value when the specified string cannot be resolved.

　　　　var exp = number (undefined); Return NaN
if (IsNaN (TMP))
{
Alert ("NaN");
}

(2). Undefined judgment: Use the typeof () method.

　　　　var exp = undefined;
if (typeof (exp) = = undefined)
{
Alert ("undefined");
}

(3). Null judgment: Use the typeof () method.

　　　　var exp = null;
if (!exp && typeof (exp)! = "undefined")
{
Alert ("is null");
}

JS data type conversion and data validity judgment