{"id":2655,"date":"2019-04-22T10:11:59","date_gmt":"2019-04-22T16:11:59","guid":{"rendered":"http:\/\/alliwalk.com\/blog\/?p=2655"},"modified":"2019-04-22T10:11:59","modified_gmt":"2019-04-22T16:11:59","slug":"learning-regular-expressions-regex","status":"publish","type":"post","link":"https:\/\/alliwalk.com\/blog\/2019\/04\/learning-regular-expressions-regex\/","title":{"rendered":"Learning Regular Expressions (regex)"},"content":{"rendered":"

Last on my list of JavaScript education\u00a0was\u00a0most recently regular expressions, which are ways for a programmer to search for strings in text. I followed FreeCodeCamp’s (FCC) curriculum. You can find more about Regular Expressions on MDN<\/a>.<\/p>\n

The short name for regular expressions is “regex”, or “regexp”. The basic outline of a ‘regex’ goes like this, which tests if “Happy” is in thisLine<\/code>:<\/p>\n

let thisLine = \"Happy happy, joy joy!\"; \r\nlet thisMatch = \/Happy\/; \r\nlet outcome = thisMatch.test(thisLine); \r\nconsole.log(outcome);<\/pre>\n
The outcome is true<\/code>. The\u00a0test<\/code>\u00a0method only results in true or false.<\/p>\n
In addition to test<\/code>, you might also use match<\/code> and replace<\/code>. I believe those are the only 3 methods<\/a> used in the FCC set of lessons.<\/p>\n
Let’s try match. If you wanted to match “Happy”, and only “Happy”, you’d write:<\/p>\n
let thisLine = \"Happy happy, joy joy!\"; \r\nlet thisMatch = \/^H[a-z]+\/; \r\nlet outcome = thisLine.match(thisMatch); \r\nconsole.log(outcome);\r\n<\/pre>\n
The outcome is [Happy]<\/code>. Probably the most important part of regex is using special characters<\/a>, and that’s what’s going on in this example. The special characters are shortcuts to help you search for a specific string. This examples searches for a string starting with a capital H (^H<\/code>) and is following by any letter from a-z ([a-z]<\/code>), and repeats the search for as long as necessary until reaching a break (like a space) (+<\/code>).<\/p>\n
An even simpler way to write the above would be to use a special character (\\w<\/code>) to search for any non-digit character and flags<\/a> to allow upper or lower case (i<\/code>), and global to search the entire string (g<\/code>).<\/p>\n
let thisLine = \"Happy happy, joy joy!\"; \r\nlet thisMatch = \/^H\\w+\/ig; \r\nlet outcome = thisLine.match(thisMatch); \r\nconsole.log(outcome);<\/pre>\n
You can also return only non-alphanumeric or digit characters.<\/p>\n
let thisLine = \"Happy happy, joy joy!\"; \r\nlet thisMatch = \/\\W+\/ig; \r\nlet outcome = thisLine.match(thisMatch); \r\nconsole.log(outcome);<\/pre>\n
The outcome is\u00a0[<\/span>\" \"<\/span>,<\/span> \", \"<\/span>,<\/span> \" \"<\/span>,<\/span> \"!\"<\/span>]<\/span><\/code><\/p>\n
There are many more examples of special characters, and I’ll be honest in admitting that I find it confusing. It took me a little while to figure out the second example above, partly because MDN separates their special characters onto different lines. Try these out in jsbin<\/a>.<\/p>\n
Anyway, regex are good to know if you need it.<\/p>\n
\n
From FreeCodeCamp:<\/p>\n
Regular expressions are special strings that represent a search pattern. Also known as “regex” or “regexp”, they help programmers match, search, and replace text. Regular expressions can appear cryptic because a few characters have special meaning. The goal is to combine the symbols and text into a pattern that matches what you want, but only what you want. This section will cover the characters, a few shortcuts, and the common uses for writing regular expressions.<\/p><\/blockquote>\n","protected":false},"excerpt":{"rendered":"
A very brief overview of regular expressions after finishing the lessons on FreeCodeCamp.org.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[4,343],"tags":[512,325,514,513,515],"_links":{"self":[{"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/posts\/2655"}],"collection":[{"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/comments?post=2655"}],"version-history":[{"count":6,"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/posts\/2655\/revisions"}],"predecessor-version":[{"id":2662,"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/posts\/2655\/revisions\/2662"}],"wp:attachment":[{"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/media?parent=2655"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/categories?post=2655"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/alliwalk.com\/blog\/wp-json\/wp\/v2\/tags?post=2655"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}