JavaScript knowledge required for GTM (Google Tag Manager)

The Google Tag Manager is a tag management system that allows you to configure and rapidly deploy tags on your website or mobile app using a simple web-based interface. It has the same capabilities as the Google Tag, a JavaScript library used to send data from your website to Google Analytics. Tag Manager also supports tag version management and organization, community and third-party-developed tag templates, enterprise collaboration tools, and security features.

JavaScript for Google Tag Manager

Before you start using the Google Tag Manager, the following JavaScript topics are necessary for you to learn ?

• Basic Syntax of JavaScript
• Data Types and Structural Types
• Functions & Scope
• String Methods
• Array Methods
• DOM Element Variable in GTM

Basic Syntax

JavaScript is a simple and dynamic computer programming language. It is used to produce dynamic client-side pages. It is a cross-platform, open-source language. Syntax is the set of rules that defines how to write your code so that it can be executed. Storage place where data are saved in JavaScript is a variable. The values are assigned to variables using the assignment operators (=, +=, %=).

Operators in JavaScript are symbols used to compute values or, to put it another way, allow us to perform operations on operands. The value is computed using the arithmetic operators (+, -, *, /). Knowledge of each of these operators and variables is necessary to use Google Tag Manager.

Suppose you need to store your first name and last name in JavaScript. For this, you first declare the variable and use assignment operator to initialize it as shown below ?

var first_name = ansh;
var last_name = kumar; 

Data Types and Structural Types

In JavaScript, the data types tell the computer about the type of data values variables are storing. Some of the predefined data types in JavaScript are strings, numbers, boolean and so on. The structural types are refers to objects and arrays, which are non-primitive and can hold collections of data values.

Functions & Scope

Multiple lines of code can be declared into a single block that we can then use or reuse across our projects with the help of a function. Sometimes they use certain values as "parameters" and then produce a certain value as a result. It is a section of the program that allows access to a variable. In other words, a variable's accessibility and visibility depend on its scope.

Given that JavaScript resembles a language from the C family, it is logical to assume that scoping in JavaScript is comparable to that in the majority of back-end programming languages, for eg. C, C++, or Java.

Syntax to define a function in JavaScript is ?

function function_name(parameters) {
  // statements
}; 

String Methods

Strings are used in JavaScript to represent and manipulate a group of characters. A string may represent both the primitive data type and an object. JavaScript automatically transforms raw strings into String objects so that even primitive strings may access and use String methods. Strings play a significant role in the Google Tag Manager code and are employed in several locations to track the HTML code for certain websites.

Name and use of some common JavaScript methods are ?

• split(): It splits a String object into an array of strings by separating it into substrings.
• substr(): It returns the characters in a string beginning at the specified location through the specified number of characters.
• slice(): It extracts and returns a section of a string.
• search():
• toString(): This method returns a string representing the specified object.

Array Methods

Any programming language can benefit greatly from using array methods. If you want to make your JavaScript code smaller and easier to understand, you must be able to use techniques like filter() and forEach(). Every element in the array is examined by the filter() method, which creates a new Array for each element that satisfies the test you provide in the callback. Each element in the array is received individually by the forEach() method, after which you may do anything you like with that element. The map() function iterates through each element of the array once more, but this time the callback's code is run against each element, and a new array is provided with the results.

DOM Element Variable in GTM

The Material Object Model (also known as the DOM) is a dynamic, hierarchical tree-like representation of the document on the website. It enables document manipulation, obtaining values for present website elements, and adding, editing, or removing others.

The page's HTML code may be seen by visiting any website and opening its source (for example, CTRL+U on Chrome (WIN)). This is the code that a programmer created to give the website its current appearance. Using the DOM to retrieve values for website elements carries significant risk. If you intend to scrape the DOM for your tracking implementation heavily, be aware that a developer may unintentionally change the website's content that breaks your GTM DOM Element variables.