javascript

Chapter 4: Variables, Scope, and Memory
window
2
color
getColor
1
return color
Figure 4 - 5
Given this search process, referencing local variables automatically stops the search from going into
another variable object. This means that identifiers in a parent context cannot be referenced if an
identifier in the local context has the same name, as in this example:
var color = “blue”;
function getColor(){
var color = “red”;
return color;
}
alert(getColor()); //”red”
In this modified code, a local variable named color is declared inside the getColor() function. When
the function is called, the variable is declared. When the second line of the function is executed, it
knows that a variable named color must be used. The search begins in the local context, where it finds
a variable named color with a value of ” red ” . Because the variable was found, the search stops and
the local variable is used, meaning that the function returns ” red ” . Any lines of code appearing after the
declaration of color as a local variable cannot access the global color variable.
Variable lookup doesn ’ t come without a price. It ’ s faster to access local variables
than global variables because there ’ s no search up the scope chain.
Garbage Collection
JavaScript is a garbage - collected language, meaning that the execution environment is responsible for
managing the memory required during code execution. In languages like C and C++, keeping track of
memory usage is a principle concern and the source of many issues for developers. JavaScript frees
developers from worrying about memory management by automatically allocating what is needed and
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