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How to: HTML, CSS, and JS

Definitions:

  • HTML is to create a structure to a page - we say what things are
  • CSS is for the style
  • Bootrap is a CSS library implemented at Twitter to create flexible templates that adapt for phones
  • JavaScript is for interaction and adding changes to the page. Changes are due to the data or user interaction

Editor

HTML

  • Core code:

    <!DOCTYPE html>
<html>

<head>
   <title>Page title</title>
</head>

<body>
    <h1>First heading</h1>
    <p>First paragraph</p1>
</body>

</html>

CSS

  • Include link to .css file in .html <head>:

    <head> 
    <link rel="stylesheet" href="style.css">
</head>

  • Different kinds of HTML selectors are called in different ways in CSS:

    • Tag selector: 
      HTML
<p>Text</p>

CSS
p {
   color: red;
}
    • Class selector (dot): 
      HTML
<p class="withborder">Text</p>

CSS
.withborder { # note the dot
   color: red;
}
    • ID selector (ashtag): 
      HTML
<h1 id="page-title">Text</h1>

CSS
#page-title { # note the #
   color: red;
}

  • Margin vs padding:

    • margin is the distance between an HTML element and the page border
    • padding is the distance between the page border and the text inside the HTML element

Bootstrap

  • There are two layouts:
    • Flexbox: divides the page in columns
    • Grid: divides the page in squares (rows and columns)

javascript

  • Variables: 
    let lastName = "Doe" # in newer js versions (var name = "John" in older js versions)  
let result = 3+2
  • Operators: 
    let result = 3+2  
let name = firstName + lastName
let result = 3 >=2 # gives true
=== equal
!== not equal
  • Functions: 
    function add(v1,v2){
  return v1+v2
}
let result = add(5,3);
  • Conditional (if): 
    let color;

if (v1===10){ 
    color = "blue"
} else {
    color = "red"
}
    can also be: 
    let color = v1 ===10? "blue" : "red"
  • Loops:
    • For: 
      for (let i=1; i<21; i+=1){
    console.log(i)
}
    • While: 
      let i=1  
while (i<21){
    console.log(i) 
    i+=1
}
    • Break: 
      let i=1  
while (true){
    console.log(i) 
    i+=1 
    if (i>21)  
        break;
}
  • Add the .js file at the end of the .html file: 
    ...
</body>  
<script src="script.js">
</script>  
</html>
  • Example 1: Writing in HTML: 
    <script>  
    let Name = "John";
    let Weight = 196;  
    let Height = 90;
    
    # write to page
    document.write (Name) # document refers to the actual HTML page. This function writes John in the rendered html page   
    # calculate bmi
    const KG_PER_KILO = 0.45
    const INCH_TO_METER = 0.0254  
    let WeightInKg = Weight * KG_PER_KILO
    let HeightInM  = Height * INCH_TO_METER  
    let BMI = WeightInKg/ HeightInM / HeightInM
    document.write (Name + ": " + BMI)
</script>
  • Example 2: Using a function: 
     <script>  
     # use data struct
     let client = { 
         Name:  "John", # let is deleted, = becomes :, and ; becomes ,
         Weight: 196,  
         Height: 90,
     }
     
     # calculate bmi with function
     const KG_PER_KILO = 0.45
     const INCH_TO_METER = 0.0254  
     function getBMI(client){
         let WeightInKg = Weight * KG_PER_KILO    # client.Weight -> client.Weight
         let HeightInM  = Height * INCH_TO_METER  # client.Height -> client.Height
         let BMI = WeightInKg/ HeightInM / HeightInM  
         return BMI
      }
     document.write (client.Name + ": " + getBMI(client))
 </script>
  • Example 3: Using arrays and loops: 
     <script>  

     # use array of structures 
     let clients = [
         { 
             Name:  "John", 
             Weight: 196,  
             Height: 90,
         },   # elements separated by comma
         { 
             Name:  "Jane", 
             Weight: 186,  
             Height: 80,
         }
     ]

     # calculate bmi with function
     const KG_PER_KILO = 0.45
     const INCH_TO_METER = 0.0254  
     function getBMI(client){
         let WeightInKg = Weight * KG_PER_KILO    # client.Weight -> client.Weight
         let HeightInM  = Height * INCH_TO_METER  # client.Height -> client.Height
         let BMI = WeightInKg/ HeightInM / HeightInM  
         return BMI
      }
      for (let i = 0; i<client.length, i++){ # arrays start from 0
            let client = clients[i];
            let bmi = getBMI(client)
            document.write (client.Name + ": " + bmi + </br>)
      }
 </script>

References

  • Information Visualization: Programming with D3.js on Coursera