JavaScript Global Objects---Common

1. Top-level functions (global functions)

1) the IsNaN () function is used to check whether its arguments are non-numeric values. -----IsNaN (x) x is a required parameter, and if X is a special non-numeric value NaN (or can be converted to such a value), the value returned is true. Returns False if X is a different value.

2) the number () function converts the value of the object to a digit. The-----Number (object) object is a must parameter, 1) if the parameter is a Date object, numbers () returns the milliseconds from January 1, 1970 to the present. 2) the number () function returns NaN if the value of the object cannot be converted to a digit.

2. Top-level properties (global properties)

1) The NaN property is used to refer to special non-numeric values.

2) The Undefined property is used to store JavaScript undefined values. Tip: You can use the = = = operation to test whether a value is undefined because the = = operator considers the undefined value equivalent to null.

For example: Var t;

if (t===undefined) {

Alert ("T is not defined!) ");

}

JavaScript Global Objects---Common