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Javascript Data structures and types
Javascript - Data structures and types
Data types
The latest ECMAScript standard defines eight data types:
- Seven data types that are primitives:
- Boolean. true and false.
- null. A special keyword denoting a null value. (Because JavaScript is case-sensitive, null is not the same as Null, NULL, or any other 3. variant.)
- undefined. A top-level property whose value is not defined.
- Number. An integer or floating point number. For example: 42 or 3.14159.
- BigInt. An integer with arbitrary precision. For example: 9007199254740992n.
- String. A sequence of characters that represent a text value. For example: “Howdy”
- Symbol (new in ECMAScript 2015). A data type whose instances are unique and immutable.
- and Object
Type Coercion
Numbers and the ‘+’ operator
In expressions involving numeric and string values with the + operator, JavaScript converts numeric values to strings.
x = 'The answer is ' + 42 // "The answer is 42"
y = 42 + ' is the answer' // "42 is the answer"
With all other operators, JavaScript does not convert numeric values to strings.
'37' - 7 // 30
'37' + 7 // "377"
when + is faced with boolean values it’s forced to convert them to numbers
1 + 1 === 2 // => true
Falsy
- 0
- ’’ or “”
- null
- undefined
- NaN
const zero = 0;
const emptyString = "";
if(!zero){
console.log("0 is falsy");
}
if(!emptyString){
console.log("An empty string is falsy")
}
console.log(NaN || 1); // => 1
console.log(null || 1); // => 1
console.log(undefined || 1); // => 1
Truthy
Every value that is not falsy is considered truthy, these include
- strings
- arrays
- objects
- functions
function somethingIsWrong(){
console.log("Something went horribly wrong")
}
function callback(){
console.log("Hello From Callback");
}
const string = "Hello world!"
const array = [1,2,3];
const object = {};
if(string){
console.log(string) // => "Hello world!"
const functionToCall = callback || somethingIsWrong
functionToCall() // => "Hello From Callback"
console.log(array || "That was not meant to happen")
console.log(object || "This is strange")
}
Converting strings to numbers
- parseInt()
- parseFloat()
parseInt only returns whole numbers, so its use is diminished for decimals
Beware of type auto converting by checking the types
const number = 21;
const string = "21"
function add100(number){
console.log(100 + number)
}
add100(number) // => 121
add100(string) // => "10021"
with type checking
const number = 21;
const string = "21"
function add100(number){
if(typeof number == "number"){
console.log(100 + number)
} else {
console.log("Need a number, not a "+typeof number);
}
}
add100(number) // => 121
add100(string) // => "Need a number, not a string"
for checking if using class
class ImportantClass {
constructor(){
this.importantValue = 1;
}
doImportantStuff(){
console.log(this.importantValue);
}
}
function useImportantClass(value){
if(value instanceof ImportantClass){
value.doImportantStuff();
} else {
console.log("Value needs to be of type ImportantClass, not "+typeof value)
}
}
const value = new ImportantStuff();
useImportantClass(value); // => 1
useImportantClass("Not important"); // => Value needs to be of type ImportantClass, not string
