This is my study book of JavaScript Definitive Guide 6th Edition.
Literals of primitive type, like strings and numbers, evalute (obviously) to the same value each time they are encountered in a program. Object literals (or initializers) such as { } and [ ] create a new object each time they are encountered. If you write var a = [] in the body of a loop, for example, each iteration of the loop will create a new empty array.
Regular expression literals are a special case. The ECMAScript 3 specification says that a RegExp literal is converted to a RegExp object when the code is parsed, and each evaluation of the code returns the same object. The ECMAScript 5 specification reverses this and requires that each evaluation of a RegExp return a new object. IE has always implemented the ECMAScript 5 behavior and most current browsers have now switched to it, even before they fully implemented the standard.
Pontuation characters with special meaning
^ $ . * + ? = ! : | \ / ( ) [ ] { }
Nongreedy and greedy repetition
Greedy repetition is things like {2}, ?, +, *, nongreedy repetition is when we use ‘combos’, like (??, +?, *? {1, 5}?)
We can group with (), also specify the match position with ^ $ \b \B
(?=p) (?!p) is positive and negative lookahead assertion but they do not include those characters in the match
In JS we have only 3 flags
- i case-insesitiive
- g global
- m multiline
String methods for pattern matching
- .search()
- .replace()
- .match()
- .join()
The RegExp object
Have four properties:
- .source read-only the regular expression
- .global read-only bool (g flag)
- .ignoreCase read-only bool (i flag)
- .multiline read-only bool (m flag)
Have 2 methods:
- .exec() (Similar to match, but a little different, it return null if find nothing and return always the same kind of array)
- .test() It takes a string and returns true if the string contains a match for the regex, calling test() is equivalent to calling exec() and returning true if the return value of exec() is not null.