The third day of JavaScript learning (Math object and regular expression)

One: The math object performs common arithmetic tasks. The commonly used math methods are:

Round (a): Rounding a

Random (): Random number (0,11)

Math.floor (Math.random () *11)

）

Max (A, b): Output a large value in a, b

Two: JavaScript RegExp object (regular expression) 1. What is REGEXP?

REGEXP is the abbreviation for regular expressions.

When you retrieve a text, you can use a pattern to describe what you want to retrieve. REGEXP is this pattern.

The simple pattern can be a single character.

More complex patterns include more characters and can be used for parsing, format checking, substitution, and so on.

You can specify the location of the search in a string, the type of character to retrieve, and so on.

2. Define RegExp

The RegExp object is used to store the retrieval mode.

Define the RegExp object with the New keyword. The following code defines the RegExp object named Patt1, whose pattern is "e":

var patt1=New RegExp ("E");

When you use the RegExp object to retrieve in a string, the character "e" is searched.

Methods for 3.REGEXP objects

The RegExp object has 3 methods: Test (), exec (), and compile ().

Test ()

The test () method retrieves the specified value in the string. The return value is true or false.

var patt1=New RegExp ("E");d ocument.write (Patt1.test (

Because the letter "E" exists in the string, the output of the above code will be:

True

EXEC ()

The EXEC () method retrieves the specified value in the string. The return value is the value that was found. If no match is found, NULL is returned.

Example 1:

var patt1=New RegExp ("E");d ocument.write (Patt1.exec (

Because the letter "E" exists in the string, the output of the above code will be:

E

Example 2:

You can add a second parameter to the RegExp object to set the retrieval. For example, if you need to find all the existence of all a character, you can use the "G" parameter ("global").

For complete information on how to modify the search mode, please visit our RegExp object reference manual.

When using the "G" parameter, the EXEC () works as follows:

• Find the first "E" and store its location
• If you run EXEC () again, retrieve it from the stored location and find the next "E" and store its location

var patt1=New RegExp ("E", "G");  Do {result=patt1.exec ("The Best Things is Free");d ocument.write (result);  while (result!=null

Because of the 6 "E" letters in this string, the output of the code will be:

Eeeeeenull

For more information, see the RegExp object reference manual.

The third day of JavaScript learning (Math object and regular expression)