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Putting this everywhere in Java code is a bad practice which reduces readability of code. The same is true with Javascript in Lightning Web Components.
But can we skip it like in Java or is there a technical reason why they are there all over in the documentation?
Extending my comments with some additional information (emphasis are all mine).
To start with, there is no similarity between Java and JavaScript except for the word "Java" in JavaScript. Both are two different languages serving different purposes.
As for the this keyword in two languages, below are some details.
By definition, Using the this Keyword in Java is used:
Within an instance method or a constructor,
thisis a reference to the current object — the object whose method or constructor is being called
The documentation further mentions as below.
The most common reason for using the
thiskeyword is because a field is shadowed by a method or constructor parameter.
In Java, you will always want to use this whenever you have a name conflict of variables/methods to avoid shadowing.
As for best practice, it usually depends on the coding practices that different organizations adapt and how frequently you use it. In my experiences with Java, I have seen people preferring to use this to explicitly call out if that was an instance variable vs. local variable. And some preferring not to have scenarios where there is a name conflict to avoid using this.
Coming to Javascript, this Keyword the link provided by @OleksandrBerehovskyi is a good starting point, which reflects the different behavior of the this keyword. There are other resources which will help you to understand the significance of this in Javascript specifically in ES6 modules used in LWC.
A very good mention about it is on the Work with Classes trailhead:
In an attempt to make JavaScript at least appear to work like a class-based language, ES6 introduced the
classkeyword....
What is important to know is that even though the
classkeyword is used, the underlying object created is still a function.
And then, the official documentation for this on MDN mentions:
A function's
thiskeyword behaves a little differently in JavaScript compared to other languages....
In most cases, the value of
thisis determined by how a function is called. It can't be set by assignment during execution, and it may be different each time the function is called.
The only time when you can skip using this in JS would be when you are say declaring local scoped variables. In all other cases you will end up using this.
I have seen people preferring to use this to explicitly call out if that was an instance variable vs. local variable - this is my practice preferring it over the m_xxxx prefix used in fflib
– cropredy
Feb 16 '19 at 0:11
This question is not specific to LWC but to JavaScript. Assuming you're specifically asking about ES6 class methods, this.foo and foo are very different things. A reference to this.foo evaluates to the instance property foo, whereas a reference to foo results in a scope chain lookup that goes all the way up to the global scope.
You should avoid building on top of your Java mental model when learning JavaScript because they are completely different under the covers.
thisin JS, like in Java. Let's wait for answers from front-end ninjas. Meanwhile this on w3schools – Oleksandr Berehovskyi Feb 15 '19 at 11:41thisis considered a bad practice in Java. You will normally want to usethiswhenever you want to avoid shadowing. Also it depends on the standards that you may be following. E.g., I have seen some company explicitly requiringthiskeyword before any check-ins. Coming to JS,thisin JS is entirely different than what is means in Java. The link provided by @OleksandrBerehovskyi is a good starting point as howthischanges its behavior. – Jayant Das Feb 15 '19 at 13:52