[TIL] 20201204 Leveling Up Our Functions

Scope

• Variable 'visibility'
• Impact of the variable
• The location where a variable is defined dictates where we have access to that variable

 

 

Function Scope

• Defined inside of a function
• Visible only inside of the function

 

 

Block Scope

• Defined inside of a block (i.e. conditionals, loops...)
• Visible only inside of the block
• If var is used to make variables, they are visible outside of the block, which is precisely why let and const are used nowadays.

 

 

Lexical Scope

• Nested functions have access to variables in their parent functions.

 

 

Function Expressions

• Creating functions with variables
• Syntax

const functionName = function() { 
    //code
}

 

 

 

Higher Order Functions

• Functions that operate on/with other functions
• Other functions can be accepted as arguments
• Can return a function
• Example

function fun1(fun) {
    fun();
    fun();
}

function fun2() {
	//code
}

fun1(fun2); //execute fun2 twice

 

 

 

Returning Functions

• Functions can be returned in other functions
• We can make a factory function that makes functions.
• Example

function makeBetweenFunc(min, max) {
    return function (num) {
    	return num >= min && num <= max;
    }
}

//returns a function that checks if a number is between min and max

 

 

 

Methods

• Functions that are properties of Objects
• Syntax

const obj = {
    func: function() {
   	//code
    }
}

• Shorthand Syntax

const obj = {
    func() {
    	//code
    }
}

 

 

 

this in Methods

• Used to access other properties on the same object.
• Example

const person = {
    first: 'Jiwan',
    last: 'Kim',
    fullName() {
    	return `&{this.first} ${this.last}`;
    }
}

• The value of this depends on the invocation contet of the function it is used in.
  • this refers to the object in front of the dot.
  • For example, for person.fullName, this means 'person'
  • By default, this refers to window object.

 

 

Try/Catch

• Syntax

try {
	//error-prone code
} catch {
	//code that runs when there's an error
}

• How to print out the error

catch(e){
    console.log(e);
}

 

 

 

 

 

* This post is a summary of Udemy Course "The Web Developer Bootcamp" by Colt Steele.