What's a ghost's favorite data type? BOOlean!
Data types are a key concept in all programming languages but today we will examine some important JavaScript data types.
- Number
The number data type represents integers or floating point numbers formatted to use a double-precision 64-bit binary format IEEE 754 value.
Double-precision floating-point format is a floating-point number format, usually occupying 64 bits in computer memory; it represents a wide dynamic range of numeric values by using a floating radix point.
let age = 37;
console.log(typeof age); => number
- String
The string data type represents a series of characters within a single ('') or double ("") quotation marks. Strings can be created as primitive values or objects using the new String() constructor.
let str = "Hello World!";
console.log(typeof str); => string
let num = 4;
console.log(typeof num); => number
num = String(num);
console.log(typeof num); => string
num = new String(num);
console.log(typeof num); => object
//Be careful not to use single ('') quotes when you
//are including an apostrophe in your string
let strApo = 'This can't work'; => SyntaxError: Unexpected identifier
let strApo = "This will fix the problem's";
- Boolean
The Boolean data type can represent two values: true or false. This is the basis for all JavaScript comparison operations and conditional test.
let booVal = true;
console.log(typeof booVal); => boolean
let numOne = 4;
let numTwo = 6;
let greatThan = numOne > numTwo;
console.log(greatThan); => false
let val = true;
if(val){
console.log("this is true");
} else {
console.log("this is false");
}; => "this is true"
- Array
The Array data type is used to store multiple data values within a single variable which can be accessed from an index starting at 0 and separated by square brackets []. They can hold different data types including functions.
[0] [1] [2] [3] [4]
let arr = [14 , "hello", true, function(a , b) { return a * b}, [3 , 4]];
//when type of is ran arrays will always show up as objects
console.log(typeof arr); => object
console.log(arr[0]); => 14
console.log(arr[3](3, 4)); => 12
console.log(arr[4][0]); => 3
- Object
The Object data type represents a collection of key-value pairs with curly brackets {}, where each key has an identifier and corresponding value of any data type.
let obj = {
firstName: 'Alex',
lastName: 'Beasley',
inSchool: true,
fullName: function(){
return this.firstName + " " + this.lastName;
}
};
console.log(typeof obj); => object
console.log(obj.fullName()); => Alex Beasley
console.log(obj.inSchool); => true
console.log(obj['firstName']); => Alex
- Undefined, null and NaN
Undefined is a data type which is a variable that has been declared but has not been assigned a specific value yet. It can also represent a function return that doesn't actually return anything. Null is the intentional absence of any object value. NaN (Not a Number) is a value that is considered not a valid number.
let testVar;
console.log(testVar); => undefined
console.log(typeof testVar); => undefined
function find(array, value){
for(let i = 0; i < array.length; i++){
if(array[i] === value){
return array[i];
}
}
return null; // if value is not found return null
}
let array = [1, 2, 3, 4]
console.log(find(array, 5)); => null
let result = 10 / 'Alex';
console.log(result); => NaN
Date types, whether privative or complex, help software devs store different kinds of information. By understanding and using JavaScripts built in data types, it will make our lives as developers much easier.
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