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

Number "NaN", "0", or the string representation of
the numeric value
Other object Value of object's toString() method if it
exists, else "undefined"
var x = "false"; // a string
if (x)
{
}
alert("x evaluated to the Boolean value true");
Since every string but the empty string ("") converts to the Boolean value of true, the
conditional is executed and the user is shown the alert.
These type conversion rules mean that comparisons such as
1 == true
0 == ""
are true. But sometimes you don‘t want type conversion to be applied when checking equality,
so JavaScript provides the strict equality operator (=). This operator evaluates to true only if its
two operands are equal and they have the same type. So, for example, the following
comparisons would be false:
1 === true
0 === ""
0 === "0"
How the JavaScript interpreter determines the type required for most operators is fairly natural
and isn‘t required knowledge for most developers. For example, when performing arithmetic,
types are converted into numbers, then computations are performed.
One important exception is the + operator. The + operator performs addition on numbers but
also serves as the concatenation operator for strings. Because string concatenation has
precedence over numeric addition, + will be interpreted as string concatenation if any of the
operands are strings. For example, both statements,
x = "2" + "3";
x = "2" + 3;
result in the assignment of the string "23" to x. The numeric 3 in the second statement is
automatically converted to a string before concatenation is applied.
Promotion of Primitive Data to Objects
It was previously mentioned that there is an object corresponding to each primitive type. These
objects provide useful methods for manipulating primitive data. For example, the String object
provides a method to convert a string to lowercase: toLowerCase(). You can invoke this
method on a String object: