Common JavaScript syntax

Variable declarations

var PI = 3.14159;
var willChange = 2;

Maybe you're wondering about value types. Read this for an explanation.

If/else statement

if (booleanExpression) {
    doSomething();
} else if (otherBooleanExpression) { 
    doSomethingElse();
} else {
    doThatLastThing();
}

While loop

while (booleanExpression) {
    doSomething();
}

For loop

for (var i = 0; i < someArray.length; i++) {
    doSomething(i);
}

Functions

function myFunction (a, b) {
    return a * b;
}

OR

var myFunction = function (a, b) {
    return a * b;
}

Please keep in mind that we can pass functions as arguments. This is a common source of confusion.

function doer (functionArg, elementArg1, elementArg2) {
  return functionArg(elementArg1, elementArg2);
}

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

function difference (a, b) {
  return a - b;
}

var a = 7,
    b = 5;

doer(sum, a, b); // returns 12
doer(difference, a, b); // returns 2

Objects

var objName = {
    key1: 1,
    schoolName: 'Queens College',
    sum: function (a, b) {
        return a + b;
    }
}

var one = objName[key1]; // note one way to access object key's
var two = 2;
var sum = objName.sum(one, two); // note the other way of accessing keys

console.log('I love ' + objName.schoolName);
// OR
console.log('I dislike ' + objName[schoolName]);