Javascript for Java developer

Comments

Java	Javascript
// single line comments /* multi line comments */ /** * Docstring * @params {String} a - blablabla */	// single line comments /* multi line comments */ /** * Docstring * @params {string} a - blablabla */

Semicolon

Java	Javascript
someStatement(); // with semicolon someStatement() // without semicolon, error	someStatement(); // with semicolon someStatement() // without semicolon, ok

Arithmetic Operator

Java	Javascript
1 + 1; // = 2 0.1 + 0.2; // = 0.30000000000000004 8 - 1 // = 7 10 * 2; // = 20 35 / 5; // = 7 5 / 2; // = 2 5f / 2f; // = 2.5f 5.0 / 2.0; // = 2.5 10 % 2; // = 0 30 % 4; // = 2	1 + 1; // = 2 0.1 + 0.2; // = 0.30000000000000004 8 - 1 // = 7 10 * 2; // = 20 35 / 5; // = 7 5 / 2; // = 2.5 5.0 / 2.0; // = 2.5 10 % 2; // = 0 30 % 4; // = 2

Semua angka di Javascript disimpan sebagai 64-bit IEEE 754 double, sedangkan Java memiliki int, float, dan double.

Precedence

Java	Javascript
(1 + 3) * 2; // = 8 2 + (2 - 1) * 8 // = 10	(1 + 3) * 2; // = 8 2 + (2 - 1) * 8 // = 10

Infinity

Java	Javascript
Double.POSITIVE_INFINITY Double.NEGATIVE_INFINITY	Infinity -Infinity

Boolean

Java	Javascript
true false	true false

String & Char

Java	Javascript
"Something" // String 'c' // char	"Something" // string 'Something' // string "s" // string 's' // string

Negation

Java	Javascript
!true // = false !false // = true	!true // = false !false // = true

Equality

Java	Javascript
1 == 1 // = true 1 != 1 // = true '1' == 1 // = error "false" == "bar" // = true "false" == false // = error "false".equals("bar") // = false	// equality check 1 == 1 // = true 1 != 1 // = true '1' == 1 // = true "false" == "bar" // = false "false" == false // = true // strict equality check 1 === 1 // = true 1 !== 1 // = true '1' === 1 // = false "false" === "bar" // = false "false" === false // = false

Comparison

Java	Javascript
1 < 10; // = true 1 > 10; // = false 2 <= 2; // = true 2 >= 2; // = true	1 < 10; // = true 1 > 10; // = false 2 <= 2; // = true 2 >= 2; // = true

String Concatenation (and more)

Java	Javascript
"Hello " + "world!"; // = "Hello world!" "1, 2, " + 3; // = "1, 2, 3"	"Hello " + "world!"; // = "Hello world!" "1, 2, " + 3; // = "1, 2, 3" "Hello " + ["world", "!"]; // = "Hello world,!" "a" < "b"; // = true
"This is a string".charAt(0); // = 'T' "Hello".length(); // = 5	"This is a string".charAt(0); // = 'T' "Hello".length; // = 5

Truthy / Falsy

Java	Javascript
null	null; undefined; // false, null, undefined, NaN, 0 and "" are falsy; everything else is truthy. // Note that 0 is falsy and "0" is truthy, even though 0 == "0".

Variables

Java	Javascript
String name = "Manusia bernapas"; int age = 12; boolean hasHighscore = true; int a = 0, b = 0, c = 0;	// 3 keywords name = "Manusia Bernapas"; var name = "Manusia Bernapas"; let name = "Manusia Bernapas"; const name = "Manusia Bernapas"; const a = 0, b = 0, c = 0;

Shorthand

Java	Javascript
i++; i--; ++i; --i; i += 1; i -= 2; i *= 3;	i++; i--; ++i; --i; i += 1; i -= 2; i *= 3;

Array / List

Java	Javascript
String[] foo = { "1", "2", "3" }; foo[2] // = "3" foo.size() // = 3 foo[2] = "4" // = { "1", "2", "4" }	const foo = ["1", 30, false]; foo[2] // = 30 foo.push("World"); foo.length; // = 4 foo[2] = 123 // = ["1", 30, 123]

Object

Java	Javascript
// sebenernya bisa pake class // tapi nanti di Javascript juga ada class yang lebih mirip // class di Javascript under the hood itu pakenya object juga // tapi dikasih syntactical sugar biar mirip kaya class biasanya	const person = { name: "Manusia Bernapas", age: 12, "has highscore": true } person.name // = "Manusia Bernapas" person.age = 20 // person.age === 20 person["has highscore"] // = true

Control Structure

Java	Javascript
int number = 2; if (number > 2) { System.out.println("Number is bigger than 2"); } else if (number == 2) { System.out.println("Number is equal to 2"); } else { System.out.println("Number is smaller or equal to 2"); }	const number = 2; if (number > 2) { console.log("Number is bigger than 2"); } else if (number === 2) { console.log("Number is equal to 2"); } else { console.log("Number is smaller or equal to 2"); }
while (condition) { // do something }	while (condition) { // do something }
do { // do something } while (condition)	do { // do something } while (condition)
for (int i = 0; i < 10; i++) { System.out.println(i); }	for (let i = 0; i < 10; i++) { console.log(i); }
char grade = 'B'; switch (grade) { case 'A': System.out.println("Great job"); break; case 'B': System.out.println("OK job"); break; case 'C': System.out.println("You can do better"); break; default: System.out.println("Oy vey"); break; }	const grade = 'B'; switch (grade) { case 'A': console.log("Great job"); break; case 'B': console.log("OK job"); break; case 'C': console.log("You can do better"); break; default: console.log("Oy vey"); break; }

Function / Method

Java	Javascript
String upper(String text) { return text.toUpperCase(); } upper("foo"); // = "FOO"	function upper(text) { return text.toUpperCase(); } upper("foo"); // = "FOO"
(String text) -> text.toUpperCase();	const upper = (text) => { return text.toUpperCase() }; const upper = (text) => text.toUpperCase(); upper("foo"); // = "FOO"
	[1, 2, 3].map((f) => f * 2) // = [2, 4, 6] [1, 2, 3].map((f) => f * 2) // = [2, 4, 6]