JavaScript CheatSheet

Copyright (c)2023 Promineo Tech
Promineo Tech Academic Team

Variable Declaration:

	var x = "value";
	let y = "value";
	const z = "value"; (constant, can not be changed)

Data Types:

• Number (e.g. 42)
• String (e.g. "Goodbye World")
• Boolean ( e.g. true/false)
• Undefined (e.g. undefined)
• Null (e.g. null)
• Object (e.g. {})
• Array (e.g. [1,2,3,4,5])

Arrays:

• Create: 

	var arr = [element1, element2, element3];

• Access: 

	arr[index];

• Update: 

	arr[index] = newElement;

• Methods: 

		• arr.push(element)
		• arr.pop()
		• arr.shift()
		• arr.unshift(element)
		• arr.slice(start, end)
		• arr.splice(index, deleteCount, element)

Operators:

• Arithmetic: +, •, *, /, % (modulo)
• Assignment: =, +=, •=, *=, /=, %=
• Comparison: ==, ===, !=, !==, >, <, >=, <=
• Logical: &&, ||, !

Control Flow:

if•else:

	if (condition) { 
		statements; 
	} else {
		statements;
	}

switch:

	switch (expression) { 
		case x: statements; 
		        break; 
		case y: statements; 
		        break; 
		default: statements; 
	}

for loop:

	for (var i = 0; i < 10; i++) { 
		statements; 
	}

while loop:

	while (condition) {
		statements;
	}

do•while loop:

	do {
		statements;	
	} while (condition);

Functions:

• Define: 

	function name(param1, param2) { statements; }

• Call: 

	name(arg1, arg2);

• Arrow function: 

	(param1, param2) => { statements; }

Objects

• Create: 

	var obj = { key1: value1, key2: value2 };

• Access: 

	obj.key1 or obj["key1"]

• Update: 

	obj.key1 = newValue;

Event Handling:

• element.addEventListener("eventType", function() { statements; });

	button.addEventListener("click", function() { alert("Button clicked!"); });

DOM Manipulation

• Get element: 

	document.getElementById("id"), document.querySelector("css selector")

• Change content: 

	element.innerHTML = "new content";

• Change style: 

	element.style.property = "new value";

String Methods

• length: 

	str.length

• concatenate: 

	str1 + str2

• indexOf: 

	str.indexOf("substring")

• slice: 

	str.slice(start, end)

• replace: 

	str.replace("old", "new")