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JavaScript

Posted by Ryan Scharfer
Ryan Scharfer
Courses Plus Student 12,537 Points

Why doesn't my global tag seem to work in this regular expression?

var myRegExp = /d/g;
var myString = "dogs and more dogs";
myRegExp.exec(myString);

Because the global "g" tag is included, I expected this to return an array with three "d"s. (Similar to what would happen with myString.match(myRegExp);) Instead I only get one. How come?

3 Answers

Chris Shaw
Chris Shaw
26,676 Points

Hi Ryan,

The exec method doesn't work in the way that most people typically expect when using the g flag, what it allows you to do is iterate over each result through a while loop whereas match searches for everything at once and returns an array. See the below link which explains in more detail about successive matches using exec.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/exec#Example.3A_Finding_successive_matches

Ryan Scharfer
PLUS
Ryan Scharfer
Courses Plus Student 12,537 Points
Ryan Scharfer
Ryan Scharfer
Courses Plus Student 12,537 Points

Thanks Chris!

Ryan Scharfer
PLUS
Ryan Scharfer
Courses Plus Student 12,537 Points
Ryan Scharfer
Ryan Scharfer
Courses Plus Student 12,537 Points

Just extra info....

I learned in the process of really trying to understand this you can set a regular expression's lastIndex property, and using the regular expression's exec method, you can get the first match of a string from a particular index. e.g.

var myRegExp = /\w+/g;
myRegExp.lastIndex = 3;
var stringToBeChecked = "apples and oranges";
myRegExp.exec(stringToBeChecked);
// returns ["les"]

This only works with the global "g" flag; otherwise the lastIndex property is ignored and "apples" is returned.

Important: lastIndex changes each time the regular expression is used