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Intermediate Express.Js: Write Conditions and Loops In The EJS (study note)


We continue to use the app.js which we have build to be the study example. In the last post, we only add a simple EJS tag <%= thingVar %> inside h1 tag. This will match the "thing" to any "thing" request from the user.

If Statement

Today, the course shows us to write a simple if statement in the EJS file. I learn to apply it to my own app.

In the if statement, if users send"/wantto/workout" request, the page will show a new content "Good Idea!".


We wrote the if statement in the "diet.ejs" file, and we add "<% %>" tags around the code. We have to wrap every line of JavaScript anytime JavaScript starts and ends.

Moreover, you may see there are two types of ejs tags here:
  • <%= %>

The one with equal sign. According to the course, when we add equal sign, the value that is returned inside of the tag will be rendered to the HTML page. it will be added to the HTML. For example, if we write <%= 10+10 %>, it will be ended up 20 in the HTML page.

  • <% %>
When we are doing logic like if statement or loops, we don't want something to be added to HTML. The logic is not supposed to display anything, so we don't use equal sign.

As the result, when we run the app, we can see "Diet Idea: workout" is equal to the "/wantto/workout" on the browser. And the page shows "Good Idea!" because the logic we set up.



For Loop

We can also write loops in the ejs file. In order to do that, we start to add a new route in the "app.js" file.

In this new route, we want to show post page when users send a "/posts" request. In the post page, it has some post titles with authors.

This route will render the new ejs file "workoutposts.ejs", and we also add {posts: posts} in side the res.render(). The first "posts" is inside the template, and the second "posts" refers to the name of variable.


Then we create a new ejs file "workoutposts.ejs".  In this file, we write a simple h1 "Workout Posts", and a for loop, which we make li for each post. 


We also need to pay attention on the ejs tags. For the for loop statement, we use "<% %>" because it is the logic. For the JavaScript inside the li, we use "<%= %>", because we want it returns the post content on the HTML page.

As the result, when I search "/posts" on the browser, it shows the list of each post title and author name in bold.

Now we have one file that is responding not only in different way depending on the variables that users pass in, but also depending on what the variables is equal to.

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