Data type conversions

Convert from a string value to a value

Usually we use functions to convert such as number (), parseint (), parsefloat ()

But we have to note that number () returns Nan if parsing a string that contains a non-numeric character. parseint () and parsefloat () ignore characters other than numbers. Returns Nan if there are only non-numeric characters in the string, or if the arguments are unreasonable.

In addition to using the relevant functions, we can also use implicit conversions. For example, using the operator "-", "*", "/", it is worth noting that "+" as a single-mesh operator can be implicitly converted (the argument is not reasonable when the return of Nan), but the binocular operator is a string connector.

If the return value is Nan, how to judge? Can be judged by the function isNaN (n).

Second, convert from numeric value to string

The method shown is n.tostring () or string (n)

The implicit approach is to use the binocular operator "+"

Three, convert to Boolean type

The Convert Boolean () is displayed, but we usually use implicit conversions.

The following values in the implicit conversion will be converted to false: numeric value 0, Nan value, null value, undefined value, empty string '

The more ingenious way is to use "!" A double negation. such as: !! 5

It should be noted that if we use the object type, we must be careful, even if it is an empty object, the return value is also true.

Iv. converting from object type to base data type

Convert to String: string (obj) is obj.tostring () "[Object Object]". This is also the case with implicit + '.

Convert to numeric value: Number (obj) is obj.valueof () if unable to convert, + (obj.tostring ())

Convert to Boolean: Boolean (obj) returns always True

Undefined value: NaN returns ' undefined '

V. Converting from a basic type to an object type

String--"string object, numeric Type-" Number object, Boolean--"Boolean object, Null value--" Error object, undefined value--"Error object

　　

　　

　　

Data type conversions