JavaScript Basic: Study Note For Boolean Logic and Logical Operators

Boolean Logic: True & False

Boolean is one of the five primitives. There are only two possible options for Boolean value: True or False.

Boolean logic is simple writing statements that evaluate to be true or false. Then, we can combine those initial statements to create more complex statement that also evaluate to true or false.

Comparison Operators

Screenshot from Udemy Course Lecture

Most of those operators are very easy to understand. I just want to mention two of them, which are "==" and "===".

Those two operators are all equal sign, but they are different. According to the course, "==" performs type coercion which means that it takes two numbers (or strings or variables) and tries to turn them into a similar type so that we can compare them.

In the meanwhile, "===" does not perform type coercion.

For example:

var x = 5;
x == "5" //true ("5" is a string. The "==" turns the string "5" to a number 5, so they can be equal. The result will be true)
x==="5" //false (The "===" can't turn string "5" to a number 5. Since these two "5" are different types, so the result is false)

Logical Operators

screenshot from Udemy course lecture

For the "&&", x<5 is true, x!==5 is false, since one true and one false, the result is false. If we want the result to be true, we need to make sure both sides are true.

For "||", one side is true, the whole thing is true. x===5 is true, so the result is true.

For "!", x===y is false, but the !(x===y) interprets x is not equal to y, so the result is true.

Truthy and Falsy Values:

According to the lecture, values that are not actually true or false, are still inherently "truthy" or "falsy" when evaluated in a Boolean context.

Falsy Values are: false, 0, '''', null, undefined, and NaN. Everything else is truthy.

When I type a "!" (Not) operator in front of each falsy values, the results are all true. Therefore, those values are fasly values.

Comments

Intermediate Express.js: How To Add Styles & Partials in EJS File?

So far, we only have simple HTML tags and ejs tags in each ejs file. Every template page has no style at all. And the basic HTML header and footer are also missing. Today, I learned how to add styles and partials in ejs file. Link Style Step One: Touch a Separate CSS file I create a new directory "Style" under the "EJSDemo" directory, then I add a new CSS file "app.css" inside "Style" folder. Step Two: Add app.use(express.static()) in the app.js I add app.use(express.static("style")) in the "app.js". This will tell Express.js to serve the content of "Style" directory. Step Three: Write styles in CSS file I simple give body an orange background color and set text color to be grey. Step Four: Link to CSS file in the EJS file I just add <link> tag to link the "app.css" file on the top of the h1 tag in each ejs template. As the result, when I run the app and...

My Story: A Mommy Start To Learn Code From Zero

From Google Image I am not a programmer, and I thought I would never become one. Everytime I see someone is coding, I think he or she must be very talent. For me, coding is a very difficult subject to learn. Not only the language has so many rules, but also the logical reasoning behind the language is complex. In my graduated school, I knew many friends who didn't have any coding background, but they are doing programmer or developer jobs now. Some of them went to school to study coding, and some of them learned to code by themselves. Their stories are so impressive. I wasn't ready to learn code until I finished my first Chinese book "留学，我的青春呀!" recently. I always want to be a writer and write my own book. I started writing blog three years ago, and I updated my post two to three times every week. As I enjoyed writing , I started to get some followers, likes, and good comments on my blog. Then, I decided to plan my first book. My First...

Seven Most Common jQuery Methods Last Part: ADD/REMOVE/TOGGLE CLASS()

Add, remove and toggleClass is also a very common way to manipulate style. .addClass() and .removeClass() I add two class selector in the style tag. Class one is to change text color to be green, and class two is change both text and background color. Now I refresh the page and change h1 text to green by using addClass() method: $("h1").addClass("one") . If you want to remove the style, you can change it to removeClass("one"). I do the same thing to the list. I change the list color and add a background color by adding the class two style value: $("li").addClass("two") . .toggleClass() According to jQuery, toggerClass method can add or remove one or more classes from each element in the set of matched elements, depending on either the class's presence or the value of the state argument. I only want to change the first list item color and background by writing: $("li").first().toggleClas...

Learn Bootcamp From Zero

Search This Blog