Intro
Today's lesson will cover the concept of logical operators, what they are and how to use them. The logic behind them is very simple. No pun intended they are called logical operators after all. View them as simple electrical circuits. There are three possible outcomes based on which current will flow through the hypothetical wires.
Again with the operators...
Last lesson we covered what operators and expressions are. Operators, just as their names state, operate on one or two values. These values must eventually be equal to a Boolean value, a simple true or false. Logical operators are, in turn, very similar to the arithmetic operators we learned about last lesson. The way they behave is at the logical level almost the same. The key exception being on what types of values the operators can be applied to.
Logical operators can be applied to Boolean values themselves. Meaning, they are used to reason with Booleans. Let's say you want to make sure both 5 is greater than 4 and 7 is less than 9. Only if both of these expressions hold true will the logical operation hold true. In another case, let's say you want to check whether 1 is equal to 2 or 7 is equal to 7. It's perfectly fine if only one of the two arithmetic expressions holds true, the logical operation will hold true.
Let's break it down. JavaScript supports three main logical operators.
- AND
- OR
- NOT
AND
In JavaScript, there are special characters which represent certain operators, in this case, logical operators. The && operator represents logical AND. This is a binary operator, and its result is true only if both the values given to it are true. By being a binary operator it takes two values.
true && false // → false
true && true // → true
OR
This logical operator is denoted by the special symbol called pipe. The pipe symbol is written like this ||. Logical OR will produce true if either of the values given to it is true.
false || true // → true
false || false // → false
NOT
NOT is very interesting. All it does is switching the value it is given. It's denoted by an exclamation mark, like this !.
!true // → false
!false // → true
This may seem funny at first, but the power of this operator is incredibly useful. You can negate whole values and expressions, and even validate their existence. This comes in handy a lot.
Mixing operators
When you mix operators, how do you know which will be executed first? Well, with arithmetic it's easy, you just follow the logic of math you learned in primary school. Multiplication and division first, then addition and subtraction. But what now? Logical operators don't exist in arithmetic. The use of operators boils down to something called precedence. Operator precedence determines which operator will be evaluated first, meaning the ones with higher precedence are the ones to be evaluated first.
Logical OR (||) has the lowest precedence, then comes logical AND (&&), then the comparison operators (>, ==, <, !=, ...), then the rest.
Here's an exercise for you to solve:
1 + 1 == 2 && 10 * 10 > 50
// what is the value of this expression?
Ternary operator
All binary operators interact with only two values, hence the name, binary. However, there is one operator in JavaScript which is ternary, and it operates on three values.
true ? 1 : 2 // → 1
false ? 1 : 2 // → 2
This is the only ternary operator in JavaScript. Often called the conditional operator, as it defines a condition to be met, based on which a result will be picked. The value on the left of the question mark picks which of the other two values will come out.
When it is true, the middle value is chosen, and when it is false, the value on the right comes out.
Summary
Great work! Logical operators are the core building blocks of any program. These expressions are used to check the validity in many parts of our programs. The true or false value dictates whether the program will continue executing or follow a totally opposite flow of control. These concepts will all be crystal clear to you in a few lessons when we get into them in more detail. Join me in the next lesson when I'll be writing about special values, and precise type comparisons
Check out previous lessons
Hope you guys and girls had as much fun reading this article as I had writing it!
Drop an upvote if you liked it, share if you believe it will be of help to someone.
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Feel free to ask any questions you have in the comments below.
Very simple to understand! I've never coded with javascript before, but definitely want to learn. I'm trying to code Alexa and most of the tutorials is in node.js. Following, looking forward to learn more!
Node is an awesome way to start. I've been using it heavily for more than a year. Nothing really compares to it, regarding simplicity and just sheet coolness factor. I'm glad you took up learning it. Stay tuned, I'll definitely be writing more lessons. I'm actually currently writing the next one. :D
Congratulations @adnanrahic
You took 90 place in my Top 100 of posts
Upvote here instead :-)
Thanks for the article. I cannot believe that logic is not taught in school maths!
Glad you liked it :).
We definitely need to push to get logic and programming incorporated into school maths. So many more kids would actually like maths if they were only given a real world representation of why it is so important.
In the UK they have recently forced the teaching of programming in schools... only to discover that most so-called ICT teachers can't program!!
Why am I not surprised. I've experienced half assed "teachers" in University, can't imagine primary school is any better. Coming across a qualified teacher is getting all the more difficult.
Really good explanation About logical operators. And I think, for ternary operators you can add some more samples, because from my experience they are more difficult than binary operators.
Also in a next article you can talk about comparison operators. :)
Thank you. I'm glad you liked the article. Actually in the second lesson I explained the basics of comparison operators. But, next lesson I'll come back to them when explaining precise comparisons. You're right about the ternary operator being a bit difficult to understand at first. I'll definitely add a more detailed example in the next lesson. :)
Nice article
i always take TRUE = 1, FALSE = 0 , AND =(Multiply), OR=(addition)
example
1*0 -> 0
which can also be
TRUE && FALSE -> FALSE
Never thought of it that way! That's a very smart solution. I'm glad you liked the article. :)
Thanks too
keep up the good work of enlightening us.
Really need hard-work to learn JavaScript!
very informative.Thanks!!
Just want to say I'm glad I found your programming blog! Thanks for the educational posts.
You're welcome! Enjoy the reading, but more importantly have fun. :)
Great and simple article for beginners to jump in and start learning :)
Thanks. I'm glad you liked it. :)
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