What do these JS shorthand characters mean?

Question

I've been trying to find out what this code means but I haven't had any luck even finding out where to start or what to look up.

if(!/^(https?):\/\//i.test(value))

I understand some of it so I've got the following questions.

what does the "/^" do?
what does the ? do?
what do the "(" and ")" do around the https
what does the ":" do?
what does the "i" do?

If this appears to be a question without research, any guidance where to start would be great.

The characters all make up a [regular expression literal](https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions). — Phylogenesis, May 28 '15 at 08:26

SharpEdge · Accepted Answer · 2015-06-01T09:31:44.013

7

What is it

A regular expression is an object that describes a pattern of characters.

Regular expressions are used to perform pattern-matching and "search-and-replace" functions on text.

This is exactly the same but maybe more clear

var patt = /^(https?):\/\//i;
if( !patt.test(value) ){
  // value DOES NOT MATCH patt!
}

What it does

In this case it checks that value doesn't start with http:// or https://

RegExp Explanation

  / //Open regexp
    ^ //Start of the string
    (  // Start of the capturing group
      https? //Match literally http or https (because s is optional "?")
    )  // End of capturing group
    :\/\/ // Match literally ://
  / // Close regexp
  i // Case-insensitive flag

Learning

Starting point: RegexOne
Testing online with RegExp Explanation: RegEx101

edited Jun 01 '15 at 09:31

answered May 28 '15 at 08:33

SharpEdge

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Down vote because of linking to W3Schools. A horrible resource for learning... – Joshua Kelly Jun 01 '15 at 08:00
I've changed to RegexOne is better now? – SharpEdge Jun 01 '15 at 09:32
Yeah, RegexOne or MDN are much better. – Joshua Kelly Jun 01 '15 at 09:34

score 1 · Answer 2 · edited May 28 '15 at 08:57

Might this help you

^ assert position at start of the string
http matches the characters http literally (case insensitive)
s? matches the character s literally (case insensitive)
Quantifier: ? Between zero and one time, as many times as possible, giving back as needed [greedy]
: matches the character : literally
\/ matches the character / literally
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])

What do these JS shorthand characters mean?

2 Answers2

What is it

What it does

RegExp Explanation

Learning