jscheatsheet 1-11

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Javascript Cheat Sheet

Basics

-On page script

 <script type="text/javascript">
 </script>

   Include external JS file

 <script src="filename.js"></script>

-Functions

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

 x = addNumbers(1, 2);

-Edit DOM element

 document.getElementByld("elementID").innerHTML = "Hello World!";

-Output

 console.log(a);              // write to the browser console
 document.write(a);           // write to the HTML
 alert(a);                    // output in an alert box
 confirm("Really?");          // yes/no dialog, returns true/false depending on user click
 prompt("Your age?","0");     // input dialog. Second argument is the initial value

-Comments

 /* Multi line
  comment */
 // One line


-If - Else                                    www.plusfeeds.com

  if ((age >= 14) && (age < 19)) {  // logical condition
    status = "Eligible.";           // executed if condition is true
  } else {                          // else block is optional
    status = "Not eligible.";       // executed if condition is false
  }

-Switch Statement

  switch (new Date().getDay()) {    // input is current day
    case 6:                         // if (day == 6)
     text = "Saturday";
     break;
    case 0:                         // if (day == 0)
     text = "Sunday";
     break;
    default:                        // else...
     text = "Whatever";
  }


-Data Types

var age = 18;                             // number
var name = "Jane";                        // string
var name = {first:"Jane", last:"Doe"};    // object
var truth = false;                        // boolean
var sheets = ("HTML","CSS","JS");         // array
var a; typeof a;                          // undefined
var a = null;                             // value null

-Objects

var student =                           // object name
 firstName:"Jane",                      // list of properties and values
 lastName:"Doe",
 age:18,
 height:170,
 fullName : function() {                // object function
  return this.firstName + " " + this.lastName;
 }


student age = 19;                       // setting value
student[age]++;                         // incrementing
name = student.fullName();              // call object function

-Loops

-For Loop
for (var i = 0; i < 10; i++){
  document.write(i + ": " + i*3 + "<br />");
}
var sum = 0;
for (var i = 0; i < a.length; i++) {
  sum + = a[i];
}                 // parsing an array
html = "";
for (var i of custOrder) {
  html += "<li>" + i + "</li>";
}

-While Loop

var i = 1;                 // initialize
while (i < 100) {          // enters the cycle if statement is
true
 i *= 2;                   // increment to avoid infinite loop
 document.write(i + ",");  // output
}

-Loops 2

-Do While Loop

var i = 1;                    // initialize
do {                          // enters cycle at least once
 i *= 2;                      // increment to avoid infinite loop
 document.write(i + ",");     // output
} while (i < 100)             // repeats cycle if statement is true at the end

-Break

for (var i = 0; i < 10; i++) {
  if (i == 5) { break; }     // stops and exits the cycle
  document.write(i + ", ");  // last output number is 4

-Continue

for (var i = 0; i < 10; i++) {
 if (i == 5) { continue; }   // skips the rest of the cycle
 document.write(i + ", ");   // skips 5
}

Variables

var a;                      // variable
var b = "init" ;            // string
var c = "Hi" + " " + "Joe"; // = "Hi Joe"
yard = 1 + 2 + "3";           = n33..
var e = [2,3,5,8];          // array
var f = false;              // boolean            Strict mode
var g = /()/;                // RegEx
var h = function(){};       // function object
const PI = 3.14;            // constant
var a = 1, b = 2, c = a + b;// one line
let z = 'zzz';              1/ block scope local vari

-Strict mode
 "use strict";    // Use strict mode to write secure code
x = 1;            // Throws an error because variable is no

-Variables 2

-Values

false, true                  // boolean
18, 3.14, Ob10011, OxF6, NaN // number
"flower", 'John'             // string
undefined, null , Infinity   // special

-Operators

a = b + c - d;               // addition, substraction
a = b * (c / d) ;             // multiplication, division
x = 100 % 48;          // modulo. 100 / 48 remainder = 4
a++; b--;              // postfix increment and decrement

Variables 3

-Bitwise operators

&     AND                             5 & 1 (0101 & 0001)    1 (1)
|     OR                              5 | 1 (0101 | 0001)    5 (101)
~     NOT                             ~5 (~0101)             10 (1010)
^     XOR                             5 ^ 1 (0101 ^ 0001)    4 (100)
<<    left shift                      5 << 1 (0101 << 1)     10 (1010)
>>    right shift                     5 >> 1 (0101 >> 1)     2 (10)
>>>   zero fill right shift           5 >>> 1 (0101 >>> 1)   2 (10)

Variables

-Arithmetic

 a * (b + c)   // grouping
 person.age    // member
 person[age]   // member
 1(a == b)     // logical not
 a != b        // not equal
 typeof a      // type (number, object, function...)
 x << 2 x >> 3 // minary shifting
 a = b         // assignment
 a == b        // equals
 a != b        // unequal
 a === b       // strict equal
 a !== b       // strict unequal
 a < b a > b   // less and greater than
 a <= b a >= b // less or equal, greater or eq
 a += b        // a = a + b (works with - * %...)
 a && b        // logical and
 a || b        // logical or

Strings

var abc = "abcdefghijklmnopqrstuvwxyz";
var esc = 'I don\'t \n know'; // \n new line
var len = abc.length;         // string length
abc.index0f("Imno");         // find substring, -1 if doesn't contain
abc.lastIndex0f("Imno");     // last occurance
abc.slice(3, 6);             // cuts out "def", negative values count from behind
abc.replace("abc","123");    // find and replace, takes regular expressions
abc.toUpperCase();          // convert to upper case
abc.toLowerCase();          // convert to lower case
abc.concat(" ", str2);      // abc + " " + str2
abc.charAt(2);              // character at index: "c"
abc[2];                    // unsafe, abc[2] = "C" doesn't work
abc.charCodeAt(2);         // character code at index: "c" -> 99
abc.split(",");            // splitting a string on commas gives an array
abc.split(""),             // splitting on characters
128.toString(16);          // number to hex(16), octal (8) or binary (2)


-Dates

Fri Jul 06 2018 04:48:33 GMT-0700 (Pacific Daylight Time)
var d = new Date();
1530877713578 miliseconds passed since 1970
Number(d)
Date("2017-06-23");                                 // date declaration
Date("2017");                                       // is set to Jan 01
Date("2017-06-23T12:00:00-09:45");                  // date - time YYYY-MM-
DDTHH:MM:SSZ
Date("June 23 2017");                               // long date format
Date("Jun 23 2017 07:45:00 GMT+0100 (Tokyo Time)"); // time zone

-Get Times

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