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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();
 

Metadata

  • Languages:
  • Published: 5th December, 2021
  • Rated: 0 out of 5 stars based on 1 ratings

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charaf ess grathjen

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