Javascript Cheat Sheet

Comments: /*Multiline *. //One Line

Functions:

function sum(a,b){ 
   return a+b;
}

Edit DOM:

document.getElementID("elementID").innerHTML = "HELLO HELLO " ;

For Loop:

for(let i=0; i< thing.length; i++){}

While Loop:

while (i< thing.length){}

Do-While Loop:

do{
  
} while(condition) 
* performs action then checkes conditional *

Switch Statements:

switch(condition) {
     case 1:
         text = "First Option";
         break;
     case 2: 
         text = "Second Option";
         break;
     default:
         text = "Default value if none of cases are hit";

Objects:

let student = {
       f_name: "Tej"
       l_name: "Charfi"
       age: 22
       height: 387 
       fullName : function() {
             return this.firstName + " " + this.lastName;
       }
};
name = student.fullName();

String Manipulation:

 \n = new Line 
 .length //string length 
 .indexOf("") //finds substring, set to -1 if not found 
 .lastIndexOf("") //finds last substring occurance of 
 .slice(num, num) // takes range 
 .replace("arg 1", "arg 2") //replaces arg 1 with arg 2 
 .charAt(x) //characters at index x 

Events

<button onclick="function();">
       Click here 
</button>

Mouse:

onclick, oncontextmenu, ondblclick, onmousedown, onmouseenter, onmouseleave, onmousemove, onmouseover, onmouseout, onmouseup

Keyboard:

onkeydown, onkeypress, onkeyup

Frame:

onabort, onbeforeunload, onerror, onhashchange, onload, onpageshow, onpagehide, onresize, onscroll, onunload

Form:

onblur, onchange, onfocus, onfocusin, onfocusout, oninput, oninvalid, onreset, onsearch, onselect, onsubmit

Drag:

ondrag, ondragend, ondragenter, ondragleave, ondragover, ondragstart, ondrop

Clipboard:

oncopy, oncut, onpaste

Media:

onabort, oncanplay, oncanplaythrough, ondurationchange, onended, onerror, onloadeddata, onloadedmetadata, onloadstart, onpause, onplay, onplaying, onprogress, onratechange, onseeked, onseeking, onstalled, onsuspend, ontimeupdate, onvolumechange, onwaiting

Animation:

animationend, animationiteration, animationstart

Misc:

transitionend, onmessage, onmousewheel, ononline, onoffline, onpopstate, onshow, onstorage, ontoggle, onwheel, ontouchcancel, ontouchend, ontouchmove, ontouchstart

Math

• .MAX_VALUE //largest possible number in JS
• /MIN_VALUE // smalles possible number in JS
• .NEGATIVE_INFINITY / .POSITIVE_INFINITY // -Infiniti and +Infinity
• .pow(x,2) //x²
• .sqrt(num)
• .abs(x) //absolute value
• .ceil // round up
• .floor //round down
• .sin / .cos / .log

Dates

var d = new Date();
a = d.getDay();     // getting the weekday

getDate();          // day as a number (1-31)
getDay();           // weekday as a number (0-6)
getFullYear();      // four digit year (yyyy)
getHours();         // hour (0-23)
getMilliseconds();  // milliseconds (0-999)
getMinutes();       // minutes (0-59)
getMonth();         // month (0-11)
getSeconds();       // seconds (0-59)
getTime();          // milliseconds since 1970

Global Functions

eval();                     // executes a string as if it was script code
String(23);                 // return string from number
(23).toString();            // return string from number
Number("23");               // return number from string
decodeURI(enc);             // decode URI. Result: "my page.asp"
encodeURI(uri);             // encode URI. Result: "my%page.asp"
decodeURIComponent(enc);    // decode a URI component
encodeURIComponent(uri);    // encode a URI component
isFinite();                 // is variable a finite, legal number
isNaN();                    // is variable an illegal number
parseFloat();               // returns floating point number of string
parseInt();                 // parses a string and returns an integer

Error Handling

try {                           // block of code to try
    undefinedFunction();
}
catch(err) {                    // handle error
    console.log(err.message);
}

Input Validation

var x = document.getElementById("mynum").value; // get input value
try { 
    if(x == "")  throw "empty";                 // error cases
    if(isNaN(x)) throw "not a number";
    x = Number(x);
    if(x > 10)   throw "too high";
}
catch(err) {                                    // if there's an error
    document.write("Input is " + err);          // output error
    console.error(err);                         // write the error in console
}
finally {
    document.write("</br />Done");              // executed regardless of the try / catch result
}

Error Name Reference:

RangeError: A number is “out of range”

ReferenceError: An illegal reference has occurred

SyntaxError: A syntax error has occurred

TypeError: A type error has occurred

URIError: An encodeURI() error has occurred