8.Regular Expression.md

#Regular Expression in JavaScript This lab is based on Chapter9: EloquentJavaScript ##Creating a regular expression There are 2 ways:

var re1 = new RegExp("abc");
var re2 = /abc/

there are some special characters such as question mark, or plus sign. If you want to use them, you have to use backslash. Like this:

var eighteen = /eighteen\+/;
var question = /question\?/;

##Testing for match Regular Express has a number of method. Simplest is test

console.log(/abc/.test("abcd"));
console.log(/abc/.test("abxde"));

Matching a set of character []: Put a set of characters between 2 square bracket

console.log(/[0123456789]/.test("1245"));
console.log(/[0-9]/.test("1");
console.log(/[0-9]/.test("acd");
console.log(/[0-9]/.test("aaascacas1"));

There are some special character:
\d Any digit character (Like [0-9])

var datetime = /\d\d-\d\d-\d\d\d\d\s\d\d:\d\d/;
console.log(datetime.test("16-06-2016 14:09"));
console.log(dateTime.test("30-jan-2003 15:20"));

\w An alphanumeric character (“word character”)

var word = /\w/;
console.log(word.test("@#@#"));

\s Any whitespace character (space, tab, newline, and similar)

var space = /\d\.\s+abc/;
console.log(space.test("1. abd"));
console.log(space.test("1.     abd"));
console.log(space.test("1.abd"));

\D A character that is not a digit

var notDigit = /\D/;
console.log(notDigit.test("ww"));
console.log(notDigit.test("1a"));
console.log(notDigit.test("1124"));

\W A nonalphanumeric character

var nonAlphanumbericChar = /\W/;
console.log(nonAlphanumbericChar.test("abc12231"));
console.log(nonAlphanumbericChar.test("!@#%{}_"));

\S A nonwhitespace character

var nonWhiteSpace = /\S/;
console.log(nonWhiteSpace.test("abc123"));
console.log(nonWhiteSpace.test("1.  abcd"));
console.log(nonWhiteSpace.test("  "));

"." Any character except for newline

var anyThing = /...\./;
console.log(anyThing.test("abc."));
console.log(anyThing.test("acbacd."));
console.log(anyThing.test("acba"));

"^" Using caret character to match any except the ones

var notBinary = /[^01]/;
console.log(notBinary.test("01101011100"));
console.log(notBinary.test("01021010010"));

##Repeating parts of Pattern The square bracket [] above only match 1 digit. How can regex match more than 1 digit?
"+" Match one or more
"*" Match zero or more

console.log(/\d+/.test(1234));
console.log(/\d+/.test());

console.log(/\d*/.test(1234));
console.log(/\d*/.test())

"?" Question mark test a character exist or not is still oke

var ball = /bal?l/;
console.log(ball.test("ball"));
console.log(ball.test("bal"));

{a,b} the character before exist from a to b times. Check datetime:

var datetime = /\d{1,2}-\d{1,2}-\d{4} \d{1,2}:\d{1,2}/;
console.log(datetime.test("20-12-2015 14:09"));

var checkTimes = /waz{3,5}up/;
console.log(checkTimes.test("wazzzzzup"));
console.log(checkTimes.test("wazzzup"));
console.log(checkTimes.test("wazup"));

##Grouping Subexpressions () using prentheses to make whole group like one character

var cartoonCrying = /boo+(hoo+)+/i; //i to match all Captalize or normal text
console.log(cartoonCrying.test("Boohoooohoohooo"));
console.log(cartoonCrying.test("boohoooohooOOO"));

##Matches and group Test is a simplest method, and it only return true or false.
exec (execute) is anther method in regex. It returns null if no match, and object if match.

var match  = /\d+/.exec("one two 100");
console.log(match);
console.log(match.input);
console.log(match.index);

if in the expression has a group subexpression, then it will return the text contain this subexpress, and the text match this subexpress:

var quotedText = /'([^']*)'/;
console.log(quotedText.exec("she said 'hello'"));

and if the subexpression appears one more times, then the result will be displayed the last match one.

console.log(/bad(ly)?/.exec("bad"));
console.log(/(\d)+/.exec("123"));

##The date type create new Date(). return the current time

var date =  new Date();
console.log(new Date(2009, 11, 9);
console.log(new Date(2009, 11, 9, 23, 59, 61));
<!--TimeStamp-->
console.log(new Date(2009, 11, 9, 23, 59, 61).getTime());
console.log(new Date(1260378001000));
<!--getFullYear, getMonth,...-->
var date = new Date();
console.log(date.getFullYear());
console.log(date.getMonth());
console.log(date.getDate());
console.log(date.getHours());
console.log(date.getMinutes());
console.log(date.getSeconds());

##Word and string boundaries

console.log(/cat/.test("concatenate"));
console.log(/cat/.test("con123cat-129e0enate"));
console.log(/\bcat\b/.test("concatenate"));
console.log(/\bcat\b/.test("con123cat-129e0enate"));

##Choice patterm Only one in the list beween the "|" match

var animalCount = /\b\d+ (pig|cow|chicken)s?\b/;
console.log(animalCount.test("15 pigs"));
console.log(animalCount.test("15 pigchickens"));

##Replace Replace will find the first match and replace.if we want to replace all matches, using "g" behind the expresssion

console.log("papa".replace("p", "m"));
console.log("Borobudur".replace(/[ou]/, "a"));
console.log("Borobudur".replace(/[ou]/g, "a"));

Replace can refer back to the matched, and using them

console.log("Le, Khanh\nNguyen, Hung\nDuong, Bach".replace(/([\w]+), ([\w]+)/g, "$1 $2"));

##Greed

function stripComments(code) {
  return code.replace(/\/\/.*|\/\*[^]*\*\//g, "");
}
console.log(stripComments("1 + /* 2 */3"));
// → 1 + 3
console.log(stripComments("x = 10;// ten!"));
// → x = 10;
console.log(stripComments("1 /* a */+/* b */ 1"));
// → 1  1

##Search method Search method return the first index if the regular expression match.
And return -1 if not found

console.log("  word".search(/\S/));
// → 2
console.log("    ".search(/\S/));
// → -1

#The last index property In the regular expression has a property is lastIndex. And when this Regex do some method, it will start from the lastIndex. And after doing something, the lastIndex will update to the behind the index of the match exec.

var pattern = /y/g;
pattern.lastIndex = 3; //lastIndex update to 3
var match = pattern.exec("xyzzy"); //lastIndex update to 5
console.log(pattern.lastIndex);

match = pattern.exec("xyzzyxxx"); //Not match any "y" from index 5
console.log(match.index);
console.log(pattern.lastIndex);

##Looping Over the Line Applying the hepoloris of lastIndex, we can using while to do something like this:

var input = "A string with 3 numbers in it... 42 and 88.";
var number = /\b(\d+)\b/g;
var match;
while (match = number.exec(input))
  console.log("Found", match[1], "at", match.index);