javascript

CHAPTER 2 ■ TYPE CONVERSION
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Figure 2–31. JavaScript does not set the i, g, or m flag when converting a string to a RegExp object.
Summary
In this chapter, you learned that JavaScript converts a string to a wrapper object whenever the string is
the left operand to the . or [] operator, quietly passing the string to the String() constructor and then
just as quietly reverting the wrapper to a string by invoking its valueOf() method. String wrappers
manipulate characters as if they were read-only elements. In other words, string values are immutable,
and wrapper methods return a new value without changing the original. So, typically you will want to
save the return value or immediately pass it to one of the operators we’ll explore in Chapter 3.
Most JavaScript operators are particular about the value type of their operands. Knowing this,
JavaScript will save the day by converting an operand of the wrong type to the correct one. Though
JavaScript does so behind the scenes, we explored how to do so by passing values to String(), Number(),
Boolean(), and Object(). If invoked without the new operator, those constructors convert their argument
to a string, number, boolean, or object. So, a string can be converted to a wrapper by passing it to
Object() without new or to String() with new:
Object("Spider-Man");
new String("Spider-Man");
So, when JavaScript creates a wrapper for a string, it’s really converting the value from the string
type to the object type. The same thing goes for number or boolean wrappers, too. Therefore, value type
conversion is vital for manipulating values with wrapper methods or with operators. You’ll learn more
about the latter in Chapter 3. Take a breather, and I’ll see you there!