Joey Javas

The JavaScript concatenation operator is the plus sign. As shown in the example below, the plus sign in JavaScript can be used to concatenate strings:

var strA = 'Joey';
var strB = 'JavaScript';
var strC = strA + ' ' + strB;
document.write(strC);//Result is Joey JavaScript

Strings can also be concatenated with the shorthand assignment operator +=, as follows:

var strA = 'Joey';
var strB = ' JavaScript';
var strC = strA += strB;
document.write(strC);//Result is Joey JavaScript

A number concatenated with a string, results in a string, as follows:

var strA = 'Joey';
var strB = 5;
var strC = strA += strB;
document.write(strC); //Result is Joey5

If two numbers are concatenated together, JavaScript is no longer concatenating, as this is now an addition operation:

var strA = 5;
var strB = 5;
var strC = strA += strB;
document.write(strC);//Result is 10

Had one or both of the numbers been in quotes, however, JavaScript will treat this as a string operation:

var strA = '5';
var strB = 5;
var strC = strA += strB;
document.write(strC);//Result is 55

To retrieve the length of a JavaScript string, access the length property of the JavaScript string object, as follows:

var strTest = 'Joey JavaScript';
document.write(strTest.length);

Note that an empty string has a length of 0.

Checking if a value is true or false is simple in JavaScript. All values evaluate to true, except for:

0
-0
null
undefined
NaN
empty string
false

For example, the following results in false being output since the empty string evaluates to false.

var testVar = ''
if (testVar)
document.write('true');
else
document.write('false');

It should also be noted that the literal strings '0' and 'false' evaluate to true.