JavaScript - Regex Match Not a Function

Question

I am trying to find a script that was loaded on the page and parse out a query parameter value from its name. My following setup has been tested and pulls out the names of all resources loaded on the page, but I run into the following error when I am trying to pull out the first instance matching my regex string. From this resource name I would like to parse out the value of an individual query string parameter found in the name.

Error:

Capture Snowplow Pixel:25 Uncaught TypeError: resourceArr.match is not a function
    at <anonymous>:25:36

Code:

//Query String Parser
var getQueryString = function ( field, url ) {
    var href = url ? url : window.location.href;
    var reg = new RegExp( '[?&]' + field + '=([^&#]*)', 'i' );
    var string = reg.exec(href);
    return string ? string[1] : null;
};

//Results Array
var resourceArr = [];

//Store Loaded Resources
var resource = window.performance.getEntriesByType("resource");

//Store Names of Loaded Resources
var resourceName = resource.forEach(function(resource){
   return resourceArr.push(resource.name);
 });

console.log(typeof resourceArr);
//RegEx Looking for Snowplow Pixel
 var re = /.*events\.fivetran\.com\/snowplow\/.*\/i\?e=pv.*/i;

//Grab First Snowplow Pixel
var snowplowPixelUrl = resourceArr.match(re);

//Store eid from Snowplow Pixel
var eid = getQueryString(eid, snowplowPixelUrl)

console.log(eid);

Resource Name Example:

https://events.fivetran.com/snowplow/2j32424h2h4/i?e=pv&url=....&eid=j2447

Answer 1

resourceArr you have is an array. match is an instance method on the String class. Maybe that's why you are getting the error saying resourceArr.match is not a function.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match

Answer 2

As I pointed out in comments, resourceArr is not a string, it's an array, so it does not have the .match() method. First you need to find a string that matches the regex, and then call .match() on it. Array.prototype.find() does just that, but to support older browsers, you need to use this polyfill . Here's how to correct your code:

var snowplowPixelUrl = resourceArr.find(function (name) {
  return re.test(name);
}).match(re);