Home HTML Data Types DOM JavaScript JS Debugging

string datatype

  • We discussed that strings store text
  • It is useful to know a few functions that can be used on string manipulation (see example below)
  • We can see the type of data using typeof operator
%%js

// assign variable
var hello = "Hello World";
console.log("variable: hello")
console.log(hello)

// seeing the type of this data
console.log("variable: hello check typeof")
console.log(typeof hello)

// add strings together
console.log("string concatenation: hello + Rohan!")
console.log(hello + " Rohan!")

.substring()

%%js
var hello = "Hello World";

// getting a certain component of this text
// (here the _ is a standin for the space character)
// H  e  l  l  o  _  W  o  r  l  d
// 0  1  2  3  4  5  6  7  8  9  10
// if we want the hello component, we want characters 0-4, so we use the following function
// (note how we use 0 and 5 as arguments, the last character is NOT INCLUSIVE)
console.log("substring: hello 0, 5")
console.log(hello.substring(0, 5))

.toUpperCase() and .toLowerCase()

%%js
var hello = "Hello World";

// useful functions to make string lowercase or uppercase
console.log("string convert to upper case: hello toUpperCase")
console.log(hello.toUpperCase())
console.log("string convert to lower case: hello toLowerCase")
console.log(hello.toLowerCase())

.includes()

%%js
var hello = "Hello World";

// useful function to check if one string is contained in another
console.log("string includes: hello includes Rohan")
console.log(hello.includes("Rohan"))
console.log("string includes: hello includes Hello")
console.log(hello.includes("Hello"))

number datatype

  • we discussed that numbers store numbers
  • here are some useful ideas in javascript to deal with numbers
%%js
console.log("Numbers info")

// assign numbers to varialbes
console.log("variable: num1")
var num1 = 9
console.log(num1)
console.log("variable: num2")
var num2 = 6
console.log(num2)


// simple operations with numbers
console.log("Operations")
console.log("subtract: num1 - num2")
console.log(num1 - num2)
console.log("add: num1 + num2")
console.log(num1 + num2)
console.log("divide: num1 / num2")
console.log(num1 / num2)
console.log("multiply: num1 * num2")
console.log(num1 * num2)
console.log("remainder (modulo): num1 % num2")
console.log(num1 % num2)

number formatting

%%js
console.log("variable: num1")
var num1 = 9
console.log(num1)
console.log("variable: num2")
var num2 = 6
console.log(num2)

// converting numbers to text
console.log("number convert string: num1")
console.log(num1.toString())

// rounding a number
console.log("round(num1 / num2)")
console.log(Math.round(num1 / num2))

// rounding a number to decimal palces
console.log("set decimals to 2 places (num1 / num2)")
console.log((num1 / num2).toFixed(2))

Array datatype

  • an array is just a list of other datatypes
  • put all the items in square brackets
  • some useful methods below
%%js
console.log("Array: assigning a list of strings")
var str1 = "1st string"
var arr_data = [str1, "2nd string", "3rd string"]
// seeing what is in the array
console.log(arr_data)

// getting one thing from an array
// "A string" "Other Data" "more data"
//    0           1            2
console.log("Array: referencing a cell #1")
console.log([ arr_data[1] ])  // zero based counting: 1 is 2nd cell

array manipulation

%%js
console.log("Array: assigning a list of strings")
var str1 = "1st string"
var arr_data = [str1, "2nd string", "3rd string"]
// seeing what is in the array
console.log(arr_data)

// adding something new to the array
console.log("Array: adding to list")
arr_data.push("4th string")
console.log(arr_data)

// removing the first element of array
console.log("Array: removing from front of list")
arr_data.shift()
console.log(arr_data)

// removing the last element of array
console.log("Array: removing from end of list")
arr_data.pop()
console.log(arr_data)

Object datatype

  • store records as key-value pairs
  • are defined by enclosing data in curly braces {}
  • allow access and modification using dot . or square bracket [] notation
%%js
console.log("Object: assigning key-value objects")
var obj = {
    name: "Safin",
    age: 13
};

// The following is stored in the object called "obj"
// {
//     name: "Safin",
//     age: 13
// }
//
// The key "name" is associated with the string value "Safin"
// The key "age" is associated with the number value 13
// Notice that keys are of the type "string"

// print obj to the console
console.log(obj);
// -> { name: 'Safin', age: 13 }
// Notice that single quotes ' and double quotes " can be used interchangeably

object access

%%js
console.log("Object: assigning key-value objects")
var obj = {
    name: "Safin",
    age: 13
};

// The following is stored in the object called "obj"
// {
//     name: "Safin",
//     age: 13
// }
//
// The key "name" is associated with the string value "Safin"
// The key "age" is associated with the number value 13
// Notice that keys are of the type "string"

// print obj to the console
console.log(obj);
// -> { name: 'Safin', age: 13 }
// Notice that single quotes ' and double quotes " can be used interchangeably

// To access certain values within an object, also known as an object's fields,
// you can use the name of the object suffixed with a dot and the name of the field
// or using the square bracket notation shown below
console.log("Object: using key name to access the name value (key notation)")
console.log(obj["name"]);
console.log("Object: using key name to access the name value (dot notation)")
console.log(obj.name);
// -> Safin

// Fields of an object can be manipulated similar to variables
console.log("Object: mutating the key name from Safin to John")
obj.name = "John"
console.log(obj);
console.log(obj.name);
// -> John

// A key-value pair can be added to the object
console.log("Object: mutating the key name from Safin to John")
obj["ghid"] = "jm1021"
console.log(obj);
// Observe new key

<IPython.core.display.Javascript object>

Hacks

Create a JavaScript snippet below with the following requirements:

  • Create an object representing yourself as a person. The object should have keys for your name, age, current classes, interests, and two more of your choosing
  • Your object must contain keys whose values are arrays. The arrays can be arrays of strings, numbers, or even other objects if you would like
  • Print the entire object with console.log after declaring it
  • Manipulate the arrays within the object and print the entire object with console.log as well as the specific changed key afterwards
  • Perform mathematical operations on fields in your object such as +, -, /, % etc. and print the results with console.log along with a message contextualizing them
  • Use typeof to determine the types of at least 3 fields in your object
%%html
<script>
console.log("This is the start of the Javascript data types hacks");
console.log("Object: assigning key-value objects");

var obj = {
    first_name: "Nitin",
    last_name: "Balaji",
    age: 15, 
    school: "Del Norte High School",
    grade: 10,
    favorite_car_brands: ["Porsche", "Audi", "Mercedes"],
    favorite_race_drivers: ["Lewis Hamilton", "Michael Schumacher", "Ayrton Senna"]
};

console.log(obj);

// Print the type of obj.age
console.log(typeof obj.age);

// Push "Lamborghini" to the favorite_car_brands array
obj.favorite_car_brands.push("Lamborghini");
console.log(obj);

// Print the type of obj.first_name and obj.favorite_race_drivers
console.log(typeof obj.first_name);
console.log(typeof obj.favorite_race_drivers);

// Increment and decrement the age
obj.age += 5;
console.log(obj);

obj.age -= 5;
console.log(obj);
</script>