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.

The JavaScript string object contains an lastIndexOf method. It returns the index in the string of the last occurrence of a specified character. The index is numbered starting at 0. For example:

var strTest = 'joey javascript';
document.write(strTest.lastIndexOf('t'));

The index returned in the preceding example is 14, as there are 15 characters in the string, “t” is the last character and the index is numbered starting at 0.

The lastIndexOf method accepts an optional second argument – the position at which to begin the search.

var strTest = 'joey javascript';
document.write(strTest.lastIndexOf('j'));

In this example the index returned is 5. Since the search starts at the end of the string and works backwards it finds the last “j”, which is at position 5 in the string. If we tell the string to start looking backwards from the second position, however, the value returned will be the “j” at position 0, as follows:

var strTest = 'joey javascript';
document.write(strTest.lastIndexOf('j',2));

Related articles:
JavaScript String Object indexOf method