Function / Scope / Arrays

I organized contents by referencing the following site: https://codecademy.com/

II. Function Declaration

1) Function Declaration

function hello() {
	console.log('Hello!');
}

hello();

1️⃣ Default parameter

function hello(name='Sally') {
	console.log('Hello' + name);
}

2️⃣ Resulting value (return)

• The default resuting value is undefined

 

2) Function Expressions

const helloMessage = function(name) {
	const message = "Hello " + name;
	return message;
};

helloMessage('Sally'); // Hello Sally

 

3) ➕ Arrow Function

• ES6 introduced arrow function syntax

const helloMessage = (name) => {
	const message = "Hello " + name;
	return message;
}; 
helloMessage('Sally'); // Hello Sally

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III. Scope

• Scope defines where variables can be accessed or referenced

 

1) Global Scope

• declared outside of blocks
• accessed from anywhere in the code
• Not recommended

 

2) Block Scope

• Accessible within {}
• Recommended

function insideBlock() {
	const greeting = 'hello';
	console.log(greeting);
}

**console.log(greeting); // ReferenceError**

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IV. Arrays

• can make arrays using an array literal []
• You can access each element using a numbered position called index
• You can also update the element by accessing an index

let greetings = ['hi', 'ciao', 'nihao'];
console.log(greetings[0]); // hi

• Arrays can store other arrays
• You can change inside values of const array
  • Because each value of const is not const
  • Each value of array is accessed through its address, not value inself
  • but cannot const array itself

 

1) Methods

• .push(values) : adds values at the end of the array
• .pop() : removes the last item from the array array
• .shift() : removes the first item from the arrray and returns the removed item
• .unshift(value or values(,)) : adds values to the first position of the array
• .splice(from, count, changed_words) : replaces values from from to the amount of count into changed_words
• .indexOf(target) : returns the index of target
• .join(' ') : returns the sum of all the elements in the array, and ' ' is added between each item.