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Javascript Basic Cheat Sheet by

Console

Print to console
consol­e.l­og(...)

Comments

One line
// single line comment
Multi lines
/*
A multi line comment
*/

Data Types

number
3, 3.1, -3.1, 3e5, 3e-5
string
"­abc­", 'abc', "­", ''
boolean
true, false
undefined
No value
null
Value of nothing
NaN
Not a number

Numbers

var x = 3.1415;
Declare a number
x.toFi­xed(2)
To string, fixed decimals
parseI­nt(­"­2")
Convert a string to int
parseF­loa­t("1.23­")
Convert a string to float

Strings

var s = "­Hel­lo"
Declare and assign a string
s.length
Length of string
s.char­At(0)
Access a character at index
s.inde­xOf­("el­")
Index of a substring
s.slice(2, 4)
Part of string (start, end)

Arithmetic Operators

+, -, *, /
Add, subtract, multiply, divide
%
Modulus (reminder)
=
Assignment
++, --
Increment, decrement
+=, -=, *=, /=, %=
Operation and assignment
?
a = (x > y)? b: c;

Compar­isons

==, !=
Equal to, not equal
===, !==
with type
>, <, >=, <=
Greate­r/Less or equal
&&, ||, !
And, Or, Not

Functions

Declare a function
function myFunc(p1, p2) {
    statements;
 ­ ­ ­ return p1 + p2;
}
Use a function
x = myFunc(1, 5);
Function variable
var f = functi­on(p1, p2) {
    statements;
    return p1 + p2;
};
Use function varialbe
x = f(1, 5);
 

Condit­ionals

if
if (x > y) {
    statements;
}
if..else
if (x > y) {
    statements;
} else {
 ­ ­ ­ ­sta­tem­ents;
}
if..else if
if (x > y) {
    statements;
} else if (x > z) {
    statements;
} else {
 ­ ­ ­ ­sta­tem­ents;
}
switch..case
switch(x) {
    case 1:
        statements;
        break;
    case 2:
        statements;
        break;
    default:
        statements;
}

Loops

while
var x = 0;
while (x < y) {
    statements;
    ++x;
}
for
for (var x = 0; x < y; ++x) {
    statements;
}
continue
Stop current iteration, continue with next one
break
Stop loop immedi­ately
for/in
var x = [ "­abc­", "­efg­", "­hij­" ];
for (i in x) {
    statements; // i = 0,1,2...
}
for/of
var x = [ "­abc­", "­efg­", "­hij­" ];
for (i of x) {
    statements; // i = "abc","efg",..
}

Arrays

var a = [8, "­hi", 6]
Declare and assign
var a = []
Declare empty array
a[0]
Extract the first element
a[0] = "­xx"
Set the first element
a.length
Length of array
a.push(17)
Add element to array
a.pop()
Remove the last element
a.splice(
 s, r,
 e1, e2..)
From index s, remove r elements, then add e1, e2...
a.forE­ach(f)
Run function f(e) for each element in array

Objects

Literal object
var x = {
  name: "cool",
  size: 10,
  sayHi = function() {
    console.log(this.name);
  }
}
Constr­uctor
function MyObj(nm) {
  this.name = nm;
  this.size = 10;
  this.sayHi = function() {
    console.log(this.name);
  }
}
Create new object
var x = new MyObj(­"­coo­l");
Use object
console.log(x.size);
x.sayHi();
 

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