Laurainda's Javascript Reference

General

Comments

// Single line comments
/* Multi line comments */

For text that acts as comments

Console log

console.log("Some text");

Display message to console, which is usually used during develpment or for debugging.

Alert

alert("Some text");

Pop up an alert box in browser.

Prompt

myAns = prompt("Question","Initial answer");

Pop up an input box in browser with initial answer (optional). Return with user input.

Declarations

Variables

var myVal;
var arr = ["arr1","arr2", "arr3"];
let myVal2 = "some value";
const PI = 3.1415;

Declare a variable. Keyword "const" has to be initialized with value, which cannot be re-assigned.

Objects

let myStruc = {
	value1=1,
	value2="two",
};
myStruc.value1 = 2;
myStruc["value2"] = "one";

Declare an object with "let". Access object properties with the bottom two lines.

Functions

function myFunction(myParam) {
	//some code...
	return "Some value";
}
myFunction("Some Parameters");

Declare and use a function. Parameters and returns are optional.

HTML DOM (Document Object Model)

Finding HTML element

myVar1 = document.getElementById(id);
myVar2 = document.getElementsByTagName(name);
myVar3 = document.getElementsByClassName(name);

Identifying HTML element by ID, name, class name

Changing HTML elements

element.attribute = new value;
element.setAttribute(attribute, value);

Changing the attribute value of an HTML element.

Create HTML element

myVar = document.createElement(element);

Create an HTML element. Need to attach it to some other element.

Add an HTML element

myElement.appendChild(newElement);

Add newElement as a child of myElement.

Delete an HTML element

myElement.removeChild(oldElement);

Remove oldElement from myElement.

Replace an HTML element

myElement.replaceChild(newElement, oldElement);

Replace oldElement with newElement.

Loops

For loop

for (var i=0; i< myMax; i++){
  // do something
}

Loop with iterations from i=0 to myMax-1.

While loop

While (i < myMax) {
  // do something
}

Evaluate i < myMax, and then do action in loop until condition becomes false.

Do While loop

do {
  // do something
} while (i < myMax)

Do actions in the loop, then evaluate whether i < myMax.

Break

while (myVar) {
  // actions 1
  break;
  //actions 2
}

Preform action 1, skip action 2, and exit loop.

Continue

while (myVar) {
  // some actions 1
  continue;
  //some actions 2
}

Preform action1, skip action 2, then go back to the top of the loop for evaluation of condition.