JS Getting Started tutorial two [isNaN () and Isfinite () []

isNaN (): is used to check whether its arguments are non-numeric values. Hint: Yes, no. (Not a number)
document.write (isNaN (0))//return False
document.write (isNaN (5-2))//return False
document.write (isNaN ("Hello"))//return True
The isfinite (number) function checks to see if its arguments are infinity.
Returns true if number is finite. Returns False if number is NaN (non-numeric) or infinity;
2): Character:
' Re right ';
In this way JS will mistakenly think that the end of the letter after you, causing errors.
So when it comes to this, escape must be used.
We can write this:
' Re right ';
In addition: You can search the escape sequence list google.com.
Simple operation Example of a string:
var a = "Cssrain";
var B = A.charat (a.length-1);  Intercepts the last character from the string A. Output: N
var c = a.substring (0, 2); Intercepts the 1th, 2 characters from the string A. Output: CS
var d = a.indexof (' s '); Finds the position of the first S occurrence from string a. Output: 1
As can be seen from the example, the cardinality starts from 0.
var e = a.substring (a.length-1); As you can see, the 2nd parameter of substring is not written,
The default is to the end.
var f = a.substring (a.length-1, a.length);//equivalent to
3): The conversion between numbers and characters:
Digit Turn character:
var number_to_string = number + ""; Method 1: Add an empty string.
var number_to_string =string (number); Method 2: Use the string () function.
var number_to_string =number. ToString (); Method 3: Use the ToString () function.
Note: the ToString () method is converted by default in 10.
If you want to use the 8 binary conversion, you can write this: number. ToString (8);
Character Spin number:
var string_to_number = string–0; Method 1: String minus 0.
var string_to_number = number (string); Method 2: Use the number () function.
var string_to_number = parseint (string); Method 3: Use the parseint () function.
String+0 can not be used in Method 1; This can result in string concatenation, not type conversions.
The number function conversion in Method 2 is very strict.
Like what:
var a = "19cssrain86";
var b = number (a); Output Nan.
If we use Method 3.
var C = parseint (a); Output 19
You can see that parseint () automatically ignores parts that are not digital.
parseint () takes only the integer part, ignoring the fractional part.
Parsefloat () will also take the decimal part of the division.
As with ToString (), parseint is also in the system, the default is 10.
If you want to use 8, you can write this: parseint ("077", 8); Output 63 = 7 * 8 + 7
When the character begins with 0, we must specify the second parameter, or JS may be converted to 8.
4): Boolean type:
Boolean in the digital environment: true converts to 1, false to 0.
In a character environment: true converts to True and false to false.
Boolean conversions:
var X_to_boolean = Boolean (x); Method 1: Use the Boolean () function.
var x_to_boolean =!x; Method 2: Use an exclamation mark.
5): Definition of function:
Method 1: Generic definition
function Square (x) {
return x*x;
}
Method 2: Function Direct Quantity definition
var square = function (x) {return x*x;} Recommended Use
Method 3: Construct parameters
var square = new Function ("X", "Return x*x;"); Low efficiency