JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

There is one further wrinkle with the + operator. Because addition and concatenation in an
expression are evaluated by the interpreter from left to right, any leading occurrences of + with
two numeric operands (or types that can be automatically converted to numbers) will be treated
as addition. For example,
var w = 5;
var x = 10;
var y = "I am string ";
var z = true;
alert(w+x+y+z);
displays the following dialog:
The addition of w and x happens before the string concatenation occurs. However, you could
force a different order of evaluation with the appropriate application of parentheses. See the
section ―Operator Precedence and Associativity‖ later in this chapter for more information.
One trick often used to force + to function as string concatenation is to use the empty string at
the beginning of the expression. For example:
var w = 5;
var x = 10;
var y = "I am string ";
var z = true;
alert(""+w+x+y+z);
The result is
To force + to operate as addition, you need to use an explicit type conversion function as
discussed in Chapter 7.